Method for entropy-encoding slice segment and apparatus therefor, and method for entropy-decoding slice segment and apparatus therefor

ABSTRACT

Provided are entropy encoding and entropy decoding for video encoding and decoding. The video entropy decoding method includes: determining a bin string and a bin index for a maximum coding unit that is obtained from a bitstream; determining a value of a syntax element by comparing the determined bin string with bin strings that is assignable to the syntax element in the bin index; storing context variables for the maximum coding unit when the syntax element is a last syntax element in the maximum coding unit, a dependent slice segment is includable in a picture in which the maximum coding unit is included, and the maximum coding unit is a last maximum coding unit in a slice segment; and restoring symbols of the maximum coding unit by using the determined value of the syntax element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/759,330, filed Jul. 6, 2015 which is a National Stage ofInternational Application No. PCT/KR2014/000093 filed on Jan. 6, 2014,claiming the benefit of U.S. Provisional Application No. 61/748,964filed on Jan. 4, 2013, the contents of which are incorporated herein byreference in their entirety.

BACKGROUND

1. Field

Methods and apparatuses consistent with exemplary embodiments relate toentropy encoding and entropy decoding for video encoding and decoding.

2. Related Art

As hardware for reproducing and storing high-resolution or high-qualityvideo content has been developed and supplied, a need for a video codecthat effectively encodes or decodes high-resolution or high-qualityvideo content has increased. Generally, a video is encoded according toa limited encoding method based on a macroblock having a predeterminedsize.

Image data of a spatial domain is transformed into coefficients of afrequency domain by using frequency transformation. A video codec splitsan image into blocks each having a predetermined size in order torapidly perform frequency transformation, performs DCT transformation oneach of the blocks, and encodes frequency coefficients in units of theblocks. The coefficients of the frequency domain may be more easilycompressed than the image data of the spatial domain. In particular,since an image pixel value of a spatial domain is expressed as aprediction error through inter prediction or intra prediction of a videocodec, when frequency transformation is performed on the predictionerror, a large data amount may be transformed into zero (0). A videocodec reduces the data amount by replacing data which is continuouslyrepeatedly generated with data having a smaller size.

Entropy encoding is performed in order to compress a bit string of asymbol generated by video encoding. Arithmetic coding-based entropyencoding has recently been widely used. In order to perform arithmeticcoding-based entropy encoding, symbols are digitized to a bit string andcontext-based arithmetic coding is performed on the bit string.

SUMMARY

Exemplary embodiments provide entropy encoding and decoding methodsusing context information of nearby data in consideration of anattribute of a slice segment, for video encoding and decoding.

According to an aspect of an exemplary embodiment, a video entropydecoding method includes: determining a bin string and a bin index for amaximum coding unit that is obtained from a bitstream; determining avalue of a syntax element by comparing the determined bin string withbin strings that may be assigned to the syntax element in the bin index;when the syntax element is a last syntax element in the maximum codingunit, a dependent slice segment may be included in a picture in whichthe maximum coding unit is included, and the maximum coding unit is alast maximum coding unit in a slice segment, storing context variablesfor the maximum coding unit; and restoring symbols of the maximum codingunit by using the determined value of the syntax element.

According to an aspect of an exemplary embodiment, a video entropydecoding method includes: determining a bin string and a bin index for amaximum coding unit that is obtained from a bitstream; determining avalue of a syntax element by comparing the determined bin string withbin strings that are assignable to the syntax element in the bin index;storing context variables for the maximum coding unit when the syntaxelement is a last syntax element in the maximum coding unit, a dependentslice segment is includable in a picture in which the maximum codingunit is included, and the maximum coding unit is a last maximum codingunit in a slice segment; and restoring symbols of the maximum codingunit by using the determined value of the syntax element.

The storing of the context variables according to various exemplaryembodiments may include storing the context variables for the maximumcoding unit when the dependent slice segment is includable in thepicture, irrespective of whether the slice segment is an independentslice segment or the dependent slice segment.

The video entropy decoding method according to various exemplaryembodiments may further include using the stored context variables forentropy decoding of a context variable of a first maximum coding unit ofthe dependent slice segment, wherein the dependent slice segment isamong slice segments included in the picture and is located next to theslice segment.

The video entropy decoding method according to various exemplaryembodiments may further include: determining whether the dependent slicesegment is includable in the picture based on first information that isobtained from a picture parameter set of the bitstream; determiningwhether the maximum coding unit is the last maximum coding unit in theslice segment based on second information that is obtained from dataabout the maximum coding unit, wherein the data about the maximum codingunit is included among data corresponding to slice segments of thebitstream; and obtaining the bin string from the data about the maximumcoding unit.

The video entropy decoding method according to various exemplaryembodiments may further include: determining a number of entry points ofsubsets that are included in the slice segment based on thirdinformation that is obtained from a slice segment header of thebitstream; determining a position of each of the entry points by usingan offset and a number indicated by fourth information, wherein theoffset is a number that is greater than the number indicated by thefourth information by 1, and the fourth information is obtained from theslice segment header of the bitstream and indicates an offset accordingto each entry point; and wherein the number of entry points and thepositions of the entry points are determined when a tile is includablein a slice segment that is included in the picture or a synchronizationoperation is performable for context variables of a maximum coding unitthat is included in the picture.

According to an aspect of an exemplary embodiment, a video entropyencoding method includes: generating a bit string of symbols that aredetermined by encoding a maximum coding unit; determining a contextvariable according to each bin index of a syntax element valuecorresponding to the symbols; determining a bin string indicating thesyntax element value based on a context value of a syntax element; andstoring context variables for the maximum coding unit when the syntaxelement is a last syntax element in the maximum coding unit, a dependentslice segment is includable in a picture in which the maximum codingunit is included, and the maximum coding unit is a last maximum codingunit in a slice segment.

The storing of the context variables according to various exemplaryembodiments may include storing the context variables for the maximumcoding unit when the dependent slice segment is includable in thepicture, irrespective of whether the slice segment is an independentslice segment or the dependent slice segment.

According to an aspect of an exemplary embodiment, a video entropydecoding apparatus includes: a context initializer that determines a binstring and a bin index for a maximum coding unit that is obtained from abitstream, and determines a value of a syntax element by comparing thedetermined bin string with bin strings that are assignable to the syntaxelement in the bin index; a context storage unit that stores contextvariables for the maximum coding unit when the syntax element is a lastsyntax element in the maximum coding unit, a dependent slice segment isincludable in a picture in which the maximum coding unit is included,and the maximum coding unit is a last maximum coding unit in a slicesegment; and a symbol restoration unit that restores symbols of themaximum coding unit by using the determined value of the syntax element.

According to an aspect of an exemplary embodiment, a video entropyencoding apparatus includes: a binarizer that generates a bit string ofsymbols that are determined by performing encoding on a maximum codingunit; a bin string determiner that determines a context value accordingto each bin index of a syntax element value corresponding to the symbolsand determines a bin string indicating the syntax element value based ona context variable of a syntax element; and a context storage unit thatstores context variables for the maximum coding unit when the syntaxelement is a last syntax element in the maximum coding unit, a dependentslice segment is includable in a picture in which the maximum codingunit is included, and the maximum coding unit is a last maximum codingunit in a slice segment.

According to an aspect of an exemplary embodiment, a computer-readablerecording medium having instructions embodied thereon a program, which,when executed by a computer performs the video entropy decoding methodis provided.

According to an aspect of an exemplary embodiment, a computer-readablerecording medium having instructions embodied thereon a program, which,when executed by a computer, performs the video entropy encoding methodis provided.

Thus, if a dependent slice segment may be used in a current picturebased on entropy encoding/decoding, a context variable may be storedafter entropy encoding (decoding) of a last maximum coding unit (LCU) ofeach slice segment is completed. Accordingly, although a previous slicesegment is an independent slice segment, an initial variable of thecontext variable that is necessary for a next dependent slice segmentmay be obtained from the context variable of the last LCU of theindependent slice segment that is previously encoded

Since information indicating a number that is less by 1 than a subsetoffset is provided through a slice segment in order to efficientlyinform of a synchronization point of a context variable for entropyencoding/decoding, a data size of the slice segment may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating a video entropy encodingapparatus according to one or more exemplary embodiments.

FIG. 1B is a flowchart of a video entropy encoding method according toone or more exemplary embodiments.

FIG. 2A is a block diagram illustrating a video entropy decodingapparatus according to one or more exemplary embodiments.

FIG. 2B is a flowchart of a video entropy decoding method according toone or more exemplary embodiments.

FIG. 3 is a diagram illustrating tiles and maximum coding units (LCUs)in a picture.

FIG. 4 is a diagram illustrating a slice segment and LCUs in a picture.

FIG. 5 is a flowchart of a context adaptive binary arithmetic coding(CABAC) parsing operation according to an exemplary embodiment.

FIG. 6A is a diagram for explaining entropy decoding using a storedcontext variable.

FIG. 6B is a detailed flowchart of an operation of storing a contextvariable in the CABAC parsing operation according to an exemplaryembodiment.

FIG. 7 is a diagram illustrating a syntax of a slice segment headeraccording to an exemplary embodiment.

FIG. 8 is a block diagram of a video encoding apparatus based on codingunits having a tree structure according to an exemplary embodiment.

FIG. 9 is a block diagram of a video decoding apparatus based on codingunits having a tree structure according to an exemplary embodiment.

FIG. 10 is a diagram for explaining a concept of coding units accordingto an exemplary embodiment.

FIG. 11 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment.

FIG. 12 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment.

FIG. 13 is a diagram illustrating deeper coding units according todepths and partitions according to an exemplary embodiment.

FIG. 14 is a diagram for explaining a relationship between a coding unitand transformation units according to an exemplary embodiment.

FIG. 15 is a diagram for explaining encoding information of coding unitscorresponding to a coded depth according to an exemplary embodiment.

FIG. 16 is a diagram illustrating deeper coding units according todepths according to an exemplary embodiment.

FIGS. 17 through 19 are diagrams for explaining a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment.

FIG. 20 is a diagram for explaining a relationship between a codingunit, a prediction unit, and a transformation unit according to codingmode information of Table 1.

FIG. 21 is a diagram illustrating a physical structure of a disc inwhich a program is stored according to an exemplary embodiment.

FIG. 22 is a diagram illustrating a disc drive for recording and readinga program by using the disc.

FIG. 23 is a diagram illustrating an overall structure of a contentsupply system for providing a content distribution service.

FIGS. 24 and 25 are diagrams illustrating an external structure and aninternal structure of a mobile phone to which a video encoding methodand a video decoding method according to an exemplary embodiment areapplied according to an exemplary embodiment.

FIG. 26 is a diagram illustrating a digital broadcasting system to whicha communication system is applied according to an exemplary embodiment.

FIG. 27 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

An entropy encoding method in a slice segment and an entropy decodingmethod in a slice segment according to various exemplary embodimentswill be explained with reference to FIGS. 1A through 7. A video encodingmethod and a video decoding method based on coding units having a treestructure according to various exemplary embodiments to which theentropy encoding method and the entropy decoding method may be appliedwill be explained with reference to FIGS. 8 through 20. In addition,various exemplary embodiments to which the video encoding method and thevideo decoding method may be applied will be explained with reference toFIGS. 21 through 27. Hereinafter, the term ‘image’ may refer to a stillimage or a moving image, that is, a video itself.

FIG. 1A is a block diagram of a video entropy encoding apparatus 10according to various exemplary embodiments.

The video entropy encoding apparatus 10 according to various exemplaryembodiments includes a binarizer 12, a bin string determiner 14, and acontext storage unit 16.

The video entropy encoding apparatus 10 may perform entropy encoding onsymbols that are encoded according to maximum coding units (LCUs). Thevideo entropy encoding apparatus 10 may store a video encoder (notshown) that performs encoding on LCUs.

A process used by the video entropy encoding apparatus 10 including thevideo encoder (not shown) to perform encoding on LCUs and generatesymbols will now be explained in detail for convenience of explanation.However, it will be understood that the video entropy encoding apparatus10 is not limited to a structure directly including the video encoder(not shown) and the video entropy encoding apparatus 10 may receivesymbols that are encoded by an external encoding apparatus.

A video encoding process according to an exemplary embodiment may bedivided into a source encoding process that minimizes redundant data dueto spatio-temporal similarity of image data and an entropy encodingprocess that minimizes redundancy again in a bit string of data that isgenerated through the source encoding process. The video entropyencoding apparatus 10 according to an exemplary embodiment performssource encoding on each of pictures that constitute a video according toblocks and generates encoded symbols. The source encoding includes aprocess of performing intra prediction/inter prediction, transformation,and quantization on video data in a space domain in units of blocks. Asa result of the source encoding, encoded symbols according to blocks maybe generated. Examples of the encoded symbols may include a quantizedtransform coefficient of a residual component, a motion vector, an intramode attribute, an inter mode attribute, and a quantization parameter.

Entropy encoding according to an exemplary embodiment may be dividedinto a binarization process that transforms symbols into a bit stringand an arithmetic encoding process that performs context-basedarithmetic coding on the bit string. Context adaptive binary arithmeticcoding (CABAC) is widely used as an encoding method that performscontext-based arithmetic coding. According to context-based arithmeticencoding/decoding, each bit of a symbol bit string may be each bin, andeach bit position may be mapped to a bin index. A length of a bitstring, that is, a length of bins, may vary according to a symbol value.For context-based arithmetic encoding/decoding, context modeling thatdetermines a context of a symbol is necessary.

For context modeling, a context needs to be newly updated for each bitposition of a symbol bit string, that is, for each bin index. The term‘context modeling’ refers to a process of analyzing a probability thateach bin is 0 or 1. A process of updating a context by reflecting aresult obtained by analyzing a probability of each of symbols of a newblock according to bits on a current context may be repeatedly performedin units of blocks. A probability table in which a probability ismatched to each bin may be provided as information containing a resultof such context modeling. Entropy coding probability informationaccording to an exemplary embodiment may be information containing aresult of context modeling.

Accordingly, once context modeling information, that is, entropy codingprobability information, is obtained, entropy encoding may be performedby assigning a code to each of bits of a binarized bit string of blocksymbols based on a context of the entropy coding probabilityinformation.

Since entropy encoding involves context-based arithmeticencoding/decoding, symbol code context information may be updated inunits of blocks, and since entropy encoding is performed by using theupdated symbol code context information, a compression ratio may beincreased.

A video encoding method according to various exemplary embodimentsshould not be construed as limited to only a video encoding methodperformed on a ‘block’ that is a data unit, and may be applied tovarious data units.

For efficiency of image encoding, an image is split into blocks eachhaving a predetermined size and then is encoded. The block may have aperfect square or rectangular shape or an arbitrary geometric shape. Thepresent exemplary embodiment is not limited a data unit having apredetermined size. The block according to an exemplary embodiment maybe an LCU, a coding unit, a prediction unit, or a transformation unit,from among coding units having a tree structure. A videoencoding/decoding method based on the coding units according to the treestructure will be explained below with reference to FIGS. 8 through 20.

Blocks of a picture are encoded in a raster scan direction.

The video entropy encoding apparatus 10 may split a picture into one ormore tiles, and each of the tiles may include blocks that are arrangedin a raster direction from among blocks of the picture. The picture maybe split into tiles that are split into one or more columns, tiles thatare split into one or more rows, or tiles that are split into one ormore columns and one or more rows. Each of the tiles may split a spatialdomain into subdomains. In order to individually encode each of thesubdomains, the video entropy encoding apparatus 10 may individuallyperform encoding in units of tiles.

Since each slice segment includes blocks that are arranged in the rasterdirection, the video entropy encoding apparatus 10 may generate a slicesegment by splitting a picture in a horizontal direction. The picturemay be split into one or more slice segments. Data of each slice segmentmay be transmitted through one network adaptation layer (NAL) unit.

The video entropy encoding apparatus 10 according to an exemplaryembodiment may perform encoding on slice segments. The video entropyencoding apparatus 10 according to an exemplary embodiment may generateencoded symbols according to blocks by sequentially performing encodingon blocks that are included in each of the slice segments. Encoded dataof blocks in each slice segment may be included in and may betransmitted through one NAL Unit. Each tile may include at least oneslice segment. If necessary, each slice segment may include at least onetile.

A slice segment may be classified into a dependent slice segment and anindependent slice segment.

If a current slice segment is a dependent slice segment, in-pictureprediction that refers to encoded symbols of a previous slice segmentthat is encoded earlier than the current slice segment may be performed.When a current slice segment is a dependent slice segment, dependententropy encoding that refers to entropy information of a previous slicesegment that is encoded earlier than the current slice segment may beperformed.

If a current slice segment is an independent slice segment, in-pictureprediction that refers to a previous slice segment is not performed andentropy information of the previous slice segment is not referred to.

One picture according to an exemplary embodiment may include oneindependent slice segment and at least one dependent segment that aresubsequent to an independent slice segment in a raster scan order. Oneindependent slice segment may be one slice.

The video entropy encoding apparatus 10 according to an exemplaryembodiment may individually perform encoding on each tile, apart fromother tiles. The video entropy encoding apparatus 10 may sequentiallyencode LCUs that are included in a current tile, according to tiles.

The video entropy encoding apparatus 10 according to an exemplaryembodiment may encode LCUs of a current slice segment according to slicesegments. LCUs that are included in a predetermined tile from among theLCUs that are included in the current slice segment may be encoded in anencoding order of a current tile.

If all of LCUs of a current slice segment belong to a current tile, thevideo entropy encoding apparatus 10 according to an exemplary embodimentmay encode the plurality of LCUs that are included in the current slicesegment in a raster scan order in the current tile. In this case, sincethe current slice segment is not located across a border of the currenttile, the LCUs of the current slice segment do not cross the border ofthe current tile. In this case, the video entropy encoding apparatus 10according to an exemplary embodiment may sequentially perform encodingon at least one slice segment that is included in each tile and mayencode a plurality of blocks that are included in each slice segment inthe raster scan order.

Even when a current slice segment includes at least one tile, the videoentropy encoding apparatus 10 may perform encoding, in a raster scanorder of LCUs of a current tile, on the LCUs that belong to the currenttile from among LCUs that are included in the current slice segment. Thevideo entropy encoding apparatus 10 according to an exemplary embodimentmay sequentially perform encoding on slice segments. Accordingly, thevideo entropy encoding apparatus 10 according to an exemplary embodimentmay generate encoded symbols according to blocks by sequentiallyperforming encoding on the slice segments and sequentially performingencoding on blocks that are included in each of the slice segments. Thevideo entropy encoding apparatus 10 may perform intra prediction, interprediction, transformation, in-loop filtering, sample adaptive offset(SAO) compensation, and quantization in units of blocks of each slicesegment.

In order to perform prediction encoding on encoded symbols that aregenerated during a source encoding process, for example, an intrasample, a motion vector, and coding mode information, in-pictureprediction may be performed. When in-picture prediction is performed, adifference value between a current encoded symbol and a previous encodedsymbol, instead of the current encoded symbol, may be encoded. Adifference value between a current sample and a neighboring sample,instead of the current sample, may be encoded.

In order to perform prediction encoding on entropy context informationor code context information that is generated during an entropy encodingprocess, dependent entropy encoding may be performed. When dependententropy encoding is performed and current entropy information andprevious entropy information are the same, encoding of the currententropy information may be omitted.

However, since the video entropy encoding apparatus 10 individuallyencodes each tile, in-picture prediction or dependent entropy encodingmay not be performed between LCUs that belong to different tiles.

The video entropy encoding apparatus 10 may record informationindicating availability of a slice segment or an attribute of the slicesegment on headers of various coding units such as a sequence parameterset (SPS), a picture parameter set (PPS), and a slice segment header.

For example, the video entropy encoding apparatus 10 may generate aslice segment header including information indicating whether a currentslice segment is an initial slice segment in a current picture.

Various basic information about a current picture to which a currentslice segment belongs may be contained in and may be transmitted througha PPS. In particular, the PPS may include information about whether thecurrent picture may include a dependent slice segment. Accordingly, wheninformation indicating that the dependent slice segment is used in thecurrent picture is contained in the PPS, the video entropy encodingapparatus 10 may include, in a current slice segment header, informationindicating whether the current slice segment is the dependent slicesegment using slice header information of a previous slice segment.

In contrast, when information indicating that a dependent slice segmentis not used in a current picture is included in a PPS of the currentpicture, information indicating whether the current slice segment is thedependent slice segment is not included in a current slice segmentheader.

When a current slice segment is not an initial slice segment, the videoentropy encoding apparatus 10 may add information indicating whether thecurrent slice segment is a dependent slice segment to a slice segmentheader.

That is, when information indicating that a dependent slice segment isused in a current picture is included in a PPS of the current pictureand information indicating that a current slice segment is not aninitial slice segment is included in a current slice segment header,information indicating whether the current slice segment is thedependent slice segment may be further added to the current slicesegment header. The initial slice segment according to an exemplaryembodiment has to be an independent slice segment. Accordingly, when thecurrent slice segment is the initial slice segment, informationindicating whether the current slice segment is the dependent slicesegments may be omitted. Accordingly, the video entropy encodingapparatus 10 may add information indicating whether the current slicesegment is the initial slice segment to the slice segment header for theinitial slice segment and then may add basic information about thecurrent slice segment to the slice segment header, and may transmitresultant information.

Accordingly, when a dependent slice segment may be used in a currentpicture and a current slice segment is not an initial slice segment,information indicating whether the current slice segment is thedependent slice segment may be further added to a current slice segmentheader.

However, when a current slice segment is a dependent slice segment, notan initial slice segment, basic information about a slice segment may bethe same as information of a previous slice segment header. Accordingly,a current slice segment header may be transmitted while includinginformation indicating whether the current slice segment is the initialslice segment and information indicating whether the current slicesegment is the dependent slice segment but omitting information that isthe same as the information of the previous slice segment header.

When a current slice segment according to an exemplary embodiment is nota dependent slice segment, a current slice segment header may includeinformation indicating whether the current slice segment is thedependent slice segment and may further include various headerinformation for the current slice segment.

The video entropy encoding apparatus 10 may contain, in a slice segmentheader, a quantization parameter and initial context information of acontext for entropy encoding and may transmit resultant information.

However, when a current slice segment is a dependent slice segment, thevideo entropy encoding apparatus 10 may perform in-picture predictionthat refers to encoded symbols of a previous slice segment that isencoded earlier than the current slice segment. When a current slicesegment is a dependent slice segment, the video entropy encodingapparatus 10 may perform dependent entropy encoding that refers toentropy information of a previous slice segment that is encoded earlierthan the current slice segment.

Accordingly, when a current slice segment is a dependent slice segment,the video entropy encoding apparatus 10 does not contain a quantizationparameter and initial context information in a slice segment header ofthe current slice segment. This is because a quantization parameter andinitial context information of the dependent slice segment may beinitialized to a quantization parameter and initial context informationthat are contained in header information of an independent slice segmentthat is previously encoded.

When a current slice segment is an independent slice segment, sincein-picture prediction is not performed, the video entropy encodingapparatus 10 may output a bit string of encoded symbols of the currentslice segment, irrespective of a previous slice segment. When a currentslice segment is an independent slice segment, the video entropyencoding apparatus 10 may output entropy information of the currentslice segment, irrespective of entropy information of a neighboringslice segment that is previously encoded. For example, when a currentslice segment is an independent slice segment, a quantization parameterand initial context information have to be contained in a current slicesegment header.

The video entropy encoding apparatus 10 may transmit a slice segmentheader and symbols of a slice segment, according to slice segments.

An operation for video entropy encoding performed by each of elements ofthe video entropy encoding apparatus 10 will now be explained in detailwith reference to FIG. 1B.

FIG. 1B is a flowchart of a video entropy encoding method according tovarious exemplary embodiments.

The video entropy encoding apparatus 10 may split a picture into atleast one slice segment, may perform encoding on each slice segment, andmay sequentially perform encoding on LCUs that are included in eachslice segment.

In operation 11, the binarizer 12 may perform binarization on symbolsthat are determined by performing encoding on an LCU to generate a bitstring of the symbols.

In operation 13, the bin string determiner 14 may determine a contextvariable according to each bin index of a syntax element valuecorresponding to the symbols of the LCU. A context variable for acurrent LCU may be determined based on a context variable according toeach bin index of a syntax element value that is used in another LCUthat is previously encoded.

Each context variable may include a context table and a context index. Acontext variable may be determined according to a syntax element.

In operation 15, the bin string determiner 14 may determine a bin stringindicating the syntax element value based on the determined contextvariable of a syntax element. The video entropy encoding apparatus 10may store data about a context table containing a correlation betweenthe bin string and a context variable for each syntax element.

The bin string determiner 14 may adopt a bin string indicated by thecontext variable that is determined in operation 13, in the contexttable for a current syntax element value.

The video entropy encoding apparatus 10 may generate a bin string forall syntax elements for the LCU, and then may determine whether to storecontext variables that are determined according to the LCU.

In operation 17, when the syntax element is a last syntax element in theLCU, a dependent slice segment may be included in a picture in which theLCU is included, and the LCU is a last LCU in a slice segment, thecontext storage unit 16 may store context variables for the LCU.

Irrespective of whether the slice segment is an independent slicesegment or a dependent slice segment, when a dependent slice segment maybe included in the picture, the context storage unit 16 may store thecontext variables for the LCU.

When a plurality of slice segments are included in the picture, forentropy encoding of a context variable of a first LCU of a dependentslice segment that is located next to a current slice segment, contextvariables that are stored in the current slice segment may be used.

The video entropy encoding apparatus 10 may generate a PPS containing aslice segment that is included in a picture, an LCU, and variousinformation that is commonly necessary to decode the LCU. The videoentropy encoding apparatus 10 may include, in the PPS, first informationindicating whether a dependent slice segment may be included in thepicture.

The video entropy encoding apparatus 10 may generate slice segment dataincluding data that is generated by encoding LCUs that are included ineach slice segment. The video entropy encoding apparatus 10 may include,in data about an LCU from among data according to slice segments, secondinformation indicating whether the LCU is a last LCU in the slicesegment. A bin string that is generated by entropy encoding may beincluded in the data about the LCU.

The video entropy encoding apparatus 10 may generate a slice segmentheader including an LCU that is included in a slice segment and variousinformation that is commonly necessary to decode LCUs. The video entropyencoding apparatus 10 may generate a bitstream including a PPS, a slicesegment header, and data according to slice segments, as a result ofencoding performed on the slice segments.

When a tile may be included in a slice segment that is included in apicture or a synchronization operation may be performed for contextvariables of an LCU that is included in the picture, the video entropyencoding apparatus 10 may include, in a slice segment header, thirdinformation indicating a number of entry points of subsets that areincluded in the slice segment and fourth information indicating a numberthat is less by 1 than an offset according to each entry point.

The term ‘subset that is included in a slice segment’ refers to a groupof LCUs that are sequentially encoded in a scan order, from among LCUsthat are included in the slice segment. Processing of the subsets may beperformed simultaneously.

A first byte of a current subset may be determined by summing subsetoffsets from a previous subset to the current subset by using the fourthinformation that is assigned to each subset. When there exist two ormore subsets, since a subset offset has to be greater than 0, the fourthinformation indicating the subset offset may be obtained by subtracting1 from the subset offset. Accordingly, an actual subset offset may be avalue that is greater by 1 than a number indicated by the fourthinformation.

An index of bytes that constitute each subset starts with 0 and a byteindex indicating a first byte is 0. Accordingly, a last byte of acurrent subset may be determined by summing a first byte of the currentsubset with a number indicated by the fourth information that isassigned to the current subset.

The video entropy encoding apparatus 10 according to an exemplaryembodiment may include a central processor (not shown) that generallycontrols the binarizer 12, the bin string determiner 14, and the contextstorage unit 16. Alternatively, each of the binarizer 12, the bin stringdeterminer 14, and the context storage unit 16 may operate due to itsown processor (not shown), and the video entropy encoding apparatus 10may generally operate as the processors (not shown) organically operate.Alternatively, the video entropy encoding apparatus 10 may operateaccording to the control of an external processor (not shown) of thevideo entropy encoding apparatus 10 according to an exemplaryembodiment.

The video entropy encoding apparatus 10 according to an exemplaryembodiment may include one or more data storage units (not shown) inwhich input/output data of the binarizer 12, the bin string determiner14, and the context storage unit 16 is stored. The video entropyencoding apparatus 10 may include a memory controller (not shown) thatcontrols data input/output of the data storage units (not shown).

FIG. 2A is a block diagram of a video entropy decoding apparatus 20according to various exemplary embodiments.

The video entropy decoding apparatus 20 according to an exemplaryembodiment includes a context initializer 22, a symbol restoration unit24 (e.g., a symbol restorer, etc.), and a context storage unit 26 (e.g.,context storage, etc.).

The video entropy decoding apparatus 20 according to an exemplaryembodiment may receive a bitstream that is generated as a result after apicture is split into two or more tiles and at least one slice segmentand then is encoded. The bitstream may be data that is generatedaccording to slice segments and may be data that is generated accordingto tiles.

Next, the video entropy decoding apparatus 20 may parse a slice segmentheader according to an attribute of a slice segment. The video entropydecoding apparatus 20 may pars information indicating whether a currentslice segment is an initial slice segment in a current picture, from theslice segment header of the current slice segment.

When it is determined from the parsed information that the current slicesegment is not the initial slice segment, the video entropy decodingapparatus 20 may further parse information indicating whether thecurrent slice segment is a dependent slice segment that uses sliceheader information of a previous slice segment, from a current slicesegment header.

However, information about whether the current picture may include thedependent slice segment may be parsed from a PPS for the current pictureto which the current slice segment belongs. Accordingly, wheninformation indicating that the dependent slice segment is used in thecurrent picture is parsed from the PPS of the current picture, the videoentropy decoding apparatus 20 may parse information indicating whetherthe current slice segment is the dependent slice segment, from thecurrent slice segment header.

In contrast, when information indicating that the dependent slicesegment is not used in the current picture is parsed from the PPS of thecurrent picture, information indicating whether the current slicesegment is the dependent slice segment is not parsed from the currentslice segment header.

Accordingly, when information indicating that the dependent slicesegment is used in the current picture is parsed from the PPS of thecurrent picture and information indicating that the current slicesegment is not the initial slice segment is parsed, the video entropydecoding apparatus 20 may further parse information indicating whetherthe current slice segment is the dependent slice segment, from thecurrent slice segment header. That is, when it is determined that thecurrent picture uses the dependent slice segment and the currentdependent slice segment is not the initial slice segment, the videoentropy decoding apparatus 20 may further parse information indicatingwhether the current slice segment is the dependent slice segment fromthe current slice segment header.

When it is determined from the parsed information that the current slicesegment is the initial slice segment, the video entropy decodingapparatus 20 does not parse information indicating whether the currentslice segment is the dependent slice segment from the current slicesegment header. Since the initial slice segment may not be the dependentslice segment, it may be determined that the initial slice segment is anindependent slice segment without the parsed information. Accordingly,when the current slice segment is the initial slice segment, the videoentropy decoding apparatus 20 may further parse information indicatingwhether the current slice segment is the initial slice segment and basicinformation about the current slice segment from an initial slicesegment header of the picture.

When it is determined from the information parsed from the current slicesegment header that the current slice segment is the dependent slicesegment, the video entropy decoding apparatus 20 may determine someheader information that is parsed from a header of a previous slicesegment as basic information of the current slice segment.

When it is determined from the information parsed from the current slicesegment header that the current slice segment is not the dependent slicesegment, the video entropy decoding apparatus 20 may parse variousheader information for the current slice segment from the current slicesegment header.

The video entropy decoding apparatus 20 may decode the current slicesegment by using the information parsed from the current slice segmentheader and symbols of the current slice segment.

When each slice segment is received through one NAL unit, the videoentropy decoding apparatus 20 may receive encoded data of blocksaccording to slice segments. Each tile may include at least one slicesegment. If necessary, a slice segment may include at least one tile. Arelationship between a slice segment and a tile is the same as thatdescribed with reference to FIGS. 1A and 1B.

The video entropy decoding apparatus 20 including the restored currentslice segment may restore at least one slice segment that is included ineach tile and may restore the picture by combining restored tiles.

The video entropy decoding apparatus 20 may parse, in a raster scanorder, symbols of a plurality of blocks that are included in the currentslice segment, according to at least one slice segment that is includedin a current tile, according to tiles. Further, the video entropydecoding apparatus 20 may decode, in the raster scan order, blocks byusing the symbols that are parsed in the raster scan order of theblocks.

The video entropy decoding apparatus 20 may parse encoded symbolsaccording to LCUs by performing entropy decoding on a bitstream of eachslice segment. The video entropy decoding apparatus 20 may parse encodedsymbols according to LCUs by sequentially performing entropy decoding onLCUs that are included in a slice segment. A process used by the videoentropy decoding apparatus 20 to perform restoration by parsing encodedsymbols according to coding units that are included in a slice segmentwill now be explained in detail with reference to FIG. 2B.

FIG. 2B is a flowchart of a video entropy decoding method according tovarious exemplary embodiments.

In operation 21, the context initializer 22 may determine a bin stringand a bin index for an LCU that is obtained from a bitstream.

The context initializer 22 may store an initialization table for aninitialization value according to each context index for each syntaxelement. According to an initialization operation of a context variable,a context index of a current syntax element may be determined to be aninitialization value based on the initialization table.

The context initializer 22 may store data about the context tablecontaining a correlation between a bin string and a context variable foreach syntax element.

The context initializer 22 may determine the context variable for eachsyntax element. Context variables of a current LCU may be synchronizedby using context variables of a nearby LCU.

In operation 23, the context initializer 22 may determine a value of asyntax element indicated by a current bin string by comparing binstrings that may be assigned to the syntax element in a current contextvariable based on the context table with the bin string in the bin indexthat is determined in operation 21.

Each context variable may be updated based on a context that is newlyaccumulated, from an initial context variable when entropy decoding ofan LCU starts, during the entropy decoding performed on bin strings forthe LCU.

The context initializer 22 may determine whether a dependent slicesegment may be included in a picture based on first information that isobtained from a PPS of the bitstream. The context initializer 22 maydetermine whether the LCU is a last LCU in a slice segment based onsecond information that is obtained from data about the LCU from amongdata according to slice segments of the bitstream. The contextinitializer 22 may obtain a bin string from the data about the LCU fromamong the data according to slice segments.

In operation 25, when the syntax element is a last syntax element in theLCU, the dependent slice segment may be included in the picture in whichthe LCU is included, and the LCU is a last LCU in the slice segment, thecontext storage unit 26 may store context variables for the LCU.

Irrespective of whether the slice segment is an independent slicesegment or a dependent slice segment, when a dependent slice segment maybe included in the picture, the context variables for the LCU may bestored.

When a plurality of slice segments are included in the picture, forentropy encoding for a context variable of a first LCU of a dependentslice segment that is located next to a current slice segment, contextvariables that is stored in the current slice segment may be used.

In operation 27, a symbol restoration unit 24 may restore symbols of theLCU by using the value of the syntax element that is determined inoperation 23.

The video entropy decoding apparatus 20 may determine a number of entrypoints of subsets that are included in the slice segment based on thirdinformation that is obtained from a slice segment header of thebitstream.

The video entropy decoding apparatus 20 may determine a position of eachof the entry points by using an offset that is a number that is greaterby 1 than a number indicated by fourth information about an offsetaccording to each entry point that is obtained from the slice segmentheader of the bitstream. Accordingly, since the video entropy decodingapparatus 20 may accurately determine an entry point for each subsetsuch as a column of slice segments, titles, or LCUs, an entropysynchronization point at which a context variable of a nearby LCU is tobe obtained may be accurately determined.

The video entropy decoding apparatus 20 may sequentially performdecoding, in a raster scan order, on each LCU by using encoded symbolsof LCUs that are parsed for each slice segment in operations 21 through27.

The video entropy decoding apparatus 20 may individually performdecoding on each tile, apart from other tiles. LCUs that are included ina current tile may be sequentially decoded according to tiles.

Accordingly, the video entropy decoding apparatus 20 may sequentiallyperform decoding, in the raster scan order, on each LCU by using encodedsymbols of LCUs that are parsed for each slice segment.

LCUs that are included in a predetermined tile from among LCUs that areincluded in a current slice segment may be decoded according to adecoding order in a current tile.

When all of LCUs of a current slice segment belong to a current tile,the video entropy decoding apparatus 20 may decode, in the raster scanorder in the current tile, the plurality of LCUs that are included inthe current slice segment. In this case, the current slice segment isnot located across a border of the current tile. The video entropydecoding apparatus 20 may sequentially decode at least one slice segmentthat is included in each tile, and may decode a plurality of blocks thatare included in each slice segment in the raster scan order.

Even when a current slice segment includes at least one tile, the videoentropy decoding apparatus 20 may perform decoding, in the raster scanorder of LCUs of a current tile in the current tile, on LCUs of thecurrent tile from among LCUs that are included in the current slicesegment.

In-picture prediction may be performed by using encoded symbols such asan intra sample that is parsed according to LCUs, a motion vector, andcoding mode information. Through the in-picture prediction, arestoration value of a current encoded symbol may be determined bysynthesizing a restoration value of a previous encoded symbol with adifference value between the current encoded symbol and the previousencoded symbol. Further, a restoration value of a current sample may bedetermined by synthesizing a restoration value of a neighboring samplethat is restored earlier than the current sample with a difference valuebetween the current sample and the previous sample.

Decoding using encoded symbols of an LCU may be performed throughinverse quantization, inverse transformation, and intraprediction/motion compensation. For example, transform coefficients oftransformation units may be restored by performing inverse quantizationon encoded symbols of each LCU, and residual information of predictionunits may be restored by performing inverse transformation on thetransform coefficients of the transformation units. Intra prediction maybe performed by using an intra sample in the residual information.Samples of a current prediction unit may be restored through motioncompensation that synthesizes the residual information with anotherrestored prediction unit indicated by the motion vector. In addition,SAO compensation and in-loop filtering may be performed on LCUs.

Accordingly, the video entropy decoding apparatus 20 may sequentiallydecode LCUs of each slice segment and each tile according to a decodingorder in a tile.

When a tile includes at least one slice segment according to anexemplary embodiment, one tile may be restored by decoding LCUs for eachslice segment and combining restoration results of slice segments.

When a slice segment includes at least one tile according to anexemplary embodiment, one slice segment may be restored by decoding LCUsfor each tile and combining restoration results of tiles.

The video entropy decoding apparatus 20 may restore a picture that iscomprised of restored tiles or restored slice segments.

According to the entropy encoding/decoding methods of FIGS. 1A, 1B, 2A,and 2B, when a dependent slice segment may be used in a current picture,after entropy encoding (decoding) of a last LCU of each slice segment iscompleted, a context variable may be stored. Accordingly, even when aprevious slice segment is an independent slice segment, an initialvariable of a context variable that is necessary for a next dependentslice segment may be obtained from a context variable of a last LCU ofan independent slice segment that is previously encoded.

Since information indicating a number that is less by 1 than a subsetoffset is provided to a slice segment in order to efficiently inform ofa synchronization point of a context variable for entropyencoding/decoding, a data size of the slice segment may be reduced.

A relationship between a slice segment and a tile that are subdomainsused by the video entropy encoding apparatus 10 and the video entropydecoding apparatus 20 according to an exemplary embodiment will now beexplained with reference to FIGS. 3 and 4.

FIG. 3 is a diagram illustrating tiles and LCUs in a picture 301.

When encoding and decoding are independently performed on each domainthat is generated by splitting the picture 301 in at least one directionfrom among a vertical direction and a horizontal direction, each domainmay be referred to as a tile. In order to perform processing in realtime by using a large amount of data of a high-definition (HD) or aultra high-definition (UHD) video, tiles may be formed by splittingpictures into at least one column and at least row and encoding/decodingmay be performed according to tiles.

Since each tile in the picture 301 is a spatial domain whereencoding/decoding is individually performed, only a tile desired to beencoded/decoded may be selectively encoded/decoded.

In FIG. 3, the picture 301 may be split into tiles by column borders 321and 323 and row borders 311 and 313. A domain surrounded by one of thecolumn borders 321 and 323 and one of the row borders 311 and 313 is atile.

When the picture 301 is split into tiles and is encoded, informationabout positions of the column borders 321 and 323 and the row borders311 and 313 may be contained in and may be transmitted through an SPS ora PPS. When the picture 301 is decoded, information about the positionsof the column borders 321 and 323 and the row borders 311 and 313 may beparsed from the SPS or the PPS, decoding may be performed on tiles andsubdomains of the picture 301 may be restored, and the subdomains may berestored to one picture 301 by using the information about the columnborders 321 and 323 and the row borders 311 and 313.

The picture 301 is split into LCUs and encoding/decoding is performed onblocks. Accordingly, each tile that is formed by splitting the picture301 by using the column borders 321 and 323 and the row borders 311 and313 may include LCUs. Since the column borders 321 and 323 and the rowborders 311 and 313 that split the picture 301 pass through bordersbetween adjacent LCUs, each LCU is not split. Accordingly, each tile mayinclude M (M is an integer) LCUs.

Accordingly, as processing is performed on tiles of the picture 301,encoding/decoding may be performed on LCUs in each tile. A number ineach LCU in FIG. 3 denotes a scan order of LCUs in a tile, that is, anorder in which processing is performed for encoding or decoding.

A tile may be different from a slice segment and a slice in thatencoding/decoding is independently performed between tiles. A slicesegment and a slice will now be explained in detail with reference toFIG. 4.

FIG. 4 is a diagram illustrating a slice segment and LCUs in a picture401.

The picture 401 is split into a plurality of LCUs. In FIG. 4, thepicture 401 is split into 13 LCUs in a horizontal direction and 9 LCUsin a vertical direction, that is, 117 LCUs in total. Each LCU may besplit into coding units having a tree structure and may beencoded/decoded.

The picture 401 is split into an upper slice and a lower slice, that is,two slices, by a border line 411. The picture 401 is split into slicesegments 431, 433, 435, and 441 by border lines 421, 423, and 411.

The slice segments 431, 433, 435, and 441 may be classified intodependent slice segments and independent slice segments. In a dependentslice segment, information that is used or generated in source encodingand entropy encoding for a predetermined slice segment may be referredto for source encoding and entropy encoding of another slice segment.Likewise, during decoding, information that is used or restored insource decoding and parsed information in entropy encoding for apredetermined slice segment from among dependent slice segments may bereferred to for entropy decoding and source decoding of another slicesegment.

In an independent slice segment, information that is used or generatedin source encoding and entropy encoding performed on slice segments isnot referred to at all and is independently encoded. Likewise, duringdecoding, for entropy decoding and source decoding of an independentslice segment, parsed information and restoration information of anotherslice segment is not used at all.

Information about whether a slice segment is a dependent slice segmentor an independent slice segment may be contained and may be transmittedthrough a slice segment header. When the picture 301 is to be decoded,information about a slice segment type may be parsed from the slicesegment header, and it may be determined whether a current slice segmentis independently decoded from another slice segment or is restored byreferring to the slice segment according to the slice segment type.

In particular, a value of syntax elements of a slice segment header ofan independent slice segment, that is, header information, may not bedetermined by being inferred from header information of a precedingslice segment. In contrast, header information of a slice segment headerof a dependent slice segment may be determined by being inferred fromheader information of a preceding slice segment.

Each slice may include N (N is an integer) LCUs. One slice may includeat least one slice segment. When one slice includes only one slicesegment, the slice may include an independent slice segment. One slicemay include one independent slice segment and at least one dependentslice segment that are subsequent to the independent slice segment. Atleast one slice segment that is included in one slice may betransmitted/received through the same access unit.

The upper slice of the picture 410 includes the slice segment 421 thatis one independent slice segment and the slice segments 433 and 435 thatare two dependent slice segments. The lower slice of the picture 410includes only the slice segment 441 that is an independent slicesegment.

A process of parsing a symbol through entropy decoding will now beexplained in detail with reference to FIGS. 5 through 7.

FIG. 5 is a flowchart of a CABAC parsing operation 50 according to anexemplary embodiment.

When the video entropy decoding apparatus 20 performs CABAC decodingaccording to an exemplary embodiment, a symbol for a predeterminedsyntax element may be parsed through the CABAC parsing operation 50.

In operation 511, the video entropy decoding apparatus 20 determineswhether a syntax element to be currently parsed is a first syntaxelement in a subset such as a column of slice segments, tiles, or LCUs,that is, a syntax element that is first parsed.

When it is determined in operation 511 that the syntax element to becurrently parsed is a first syntax element, the CABAC parsing operation50 proceeds to operation 513. In operation 513, a context internalvariable is initialized. The context internal variable may be a contextindex and a context table for a current syntax element. The contextinternal variable may be determined to be a preset default value.

In operation 521, the video entropy decoding apparatus 20 may obtain abin string indicating the current syntax element from a bitstream. Inoperations 523 and 525, a first bin index of the bin string may be setto −1, and a bin index may increase by 1 whenever one bit is added tothe bin string.

In operation 527, the video entropy decoding apparatus 20 may obtain acontext variable corresponding to a current bin index of the syntaxelement. For example, the context variable corresponding to the currentbin index may include a context table, a context index, and a bypassflag. Preset data about a context variable may be previously stored inthe video entropy decoding apparatus 20 to correspond to each bin indexof each syntax element. A context variable corresponding to a bin indexof the current syntax element may be selected based on the previouslystored data.

In operation 529, the video entropy decoding apparatus 20 may decode abit string corresponding to the context variable of the bin string. Abypass state that is assigned to the current bin index may be determinedbased on data about a bypass flag that is preset according to each binindex according to syntax elements. A context index may be determinedbased on an attribute (e.g., a scan index of a data unit, a colorcomponent index, or a size of a data unit) or a current state of a dataunit (e.g., a coding unit, a transformation unit, or a prediction unit)that is currently encoded according to each syntax element. A bit stringcorresponding to a current context index and a bypass state may bedetermined in a context table.

In operation 531, the video entropy decoding apparatus 20 may comparedata that contains a bit string that is available in the current syntaxelement with a current bit string that is determined in operation 529.When the current bit string does not belong to bit string data, theCABAC parsing operation 50 may return to operation 525 to increase thebin index by 1 and operations 527 and 529 to determine a contextvariable for a bin string obtained by adding one bit and decode a bitstring.

When it is determined in operation 531 that the current bit string thatis determined in operation 529 belongs to bit string data for the syntaxelement, the CABAC parsing operation 50 proceeds to operation 533. Inoperation 533, it may be determined whether the current syntax elementis information ‘pcm_flag’ indicating a PCM mode and a syntax elementvalue indicates the PCM mode. When it is determined in operation 529that a unit is an LCU in the PCM mode, the CABAC parsing operation 50proceeds to operation 535. In operation 535, the CABAC parsing operation50 may be initialized.

When it is determined in operation 533 that a mode is not the PCM mode,the CABAC parsing operation 50 proceeds to operation 537. In operation537, it may be determined whether the current syntax element is a lastsyntax element in a current subset (e.g., an LCU or a slice segment),that is, is an object to be last parsed. When it is determined inoperation 537 that the current syntax element is a last syntax element,the CABAC parsing operation 50 proceeds to operation 539. In operation539, a context variable that is finally updated in a current LCU may bestored.

When the storing of the context variable is completed or the currentsyntax element is not a last syntax element, a process of parsing thecurrent syntax element may end.

The context variable that is stored in operation 539 may be used forentropy decoding of another subset. FIG. 6A is a diagram for explainingentropy decoding using a stored context variable.

When a subset is each LCU row, an initial context variable of a currentLCU row may be determined by using a final context variable of aprevious LCU row.

For example, an initial context variable of a first LCU of a current LCUrow in an image 60 may be determined to be, that is, may be synchronizedwith, a final context variable of a last LCU of an LCU row that islocated right over the current LCU row. Accordingly, while an initialcontext variable of a first LCU 61 of a first LCU row may be set to adefault context variable, an initial context variable 631 of a first LCU63 of a second LCU row may be determined to be a final context variable629 of a last LCU 62 of the first LCU row, and an initial contextvariable 651 of a first LCU 66 of a third LCU row may be determined tobe a final context variable 649 of a last LCU 64 of the second LCU row.

If a synchronization distance is 1, for synchronization of a contextvariable of a current LCU, the context storage unit 26 may use a contextvariable of a second LCU of an upper LCU row. Accordingly, when updatingof the second LCU of the upper LCU row is completed and a final contextvariable is determined, the final context variable may be stored, and acontext variable of an LCU of a current LCU row may be determined byusing the stored final context variable of the upper LCU row.

FIG. 6B is a detailed flowchart of operation 539 of storing a contextvariable in the CABAC parsing operation 50 according to an exemplaryembodiment.

In operation 551, the context storage unit 16 or 26 may determinewhether a current LCU is a second LCU in a current subset andsynchronization of a context variable has to be performed in a currentpicture. When it is determined in operation 551 that synchronization ofthe context variable is needed and the current LCU is a second LCU,operation 539 proceeds to operation 553. In operation 553, the contextstorage unit 16 or 26 may store a final context variable of the currentLCU for wavefront parallel processing (WPP). In WPP, when asynchronization distance is 1 as shown in FIG. 6A, a context variable ofa first LCU of a current LCU row may be synchronized with a contextvariable that is stored in a second LCU of an upper LCU row.

In operation 561, the context storage unit 16 or 26 may determinewhether the current LCU is a last LCU in a current slice segment and adependent slice segment may exist in the current picture. When it isdetermined in operation 561 that the dependent slice segment may existand the current slice segment is a last slice segment, operation 539 mayproceed to operation 563. In operation 563, the context storage unit 16or 26 may store a final context variable of the current LCU for thedependent slice segment that is subsequent.

FIG. 7 is a diagram illustrating a syntax of a slice segment header 71according to an exemplary embodiment.

The video entropy decoding apparatus 20 may obtain information aboutentry point offsets of a current slice segment from the slice segmentheader 71. In detail, in information 72, when a slice segment in apicture in which the current slice segment is included satisfies atleast one condition from among a condition for a possibility‘tiles_enabled_flag’ that a tile exists and a condition for apossibility ‘entropy_coding_sync_enabled_flag’ that a context variableis synchronized according to LCUs, the slice segment header 71 maycontain information 73 ‘num_entry_point_offsets’ indicating a number ofentry points of subsets that are included in the current slice segment.Information ‘entry_point_offset_minus1[i]’ 75 indicating a number thatis less by 1 than an offset according to each actual entry point foreach entry point 74 may be assigned according to the entry points.

When two or more subsets exist, since a subset offset has to be greaterthan 0, entry point offset information ‘entry_point_offset_minus1[i]’may be obtained by subtracting 1 from an actual subset offset.Accordingly, the actual subset offset may be a value that is greater by1 than a number indicated by the entry point offset information‘entry_point_offset_minus1[i]’.

A first byte of a current subset may be determined by summing subsetoffsets from a previous subset to a current subset by using the entrypoint offset information ‘entry_point_offset_minus1[i]’ that is assignedto each subset. Accordingly, a value obtained after summing values thatare greater by 1 than a number indicated by the entry point offsetinformation ‘entry_point_offset_minus1[i]’ of subsets from the previoussubset to the current subset may be determined as a first byte of thecurrent subset.

An index of bytes that constitute each subset starts with 0, and a byteindex indicating a first byte is 0. Accordingly, a last byte of thecurrent subset may be determined by summing the first byte of thecurrent subset with a number indicated by the entry point offsetinformation ‘entry_point_offset_minus1[i]’ that is assigned to thecurrent subset.

In the video entropy encoding apparatus 10 according to an exemplaryembodiment and the video entropy decoding apparatus 20 according to anexemplary embodiment, blocks into which video data is split are LCUs andeach of the LCUs is split into coding units having a tree structure asdescribed above. A video encoding method and apparatus and a videdecoding method and apparatus based on an LCU and coding units having atree structure according to an exemplary embodiment will now beexplained with reference to FIGS. 8 through 20.

FIG. 8 is a block diagram of a video encoding apparatus 100 based oncoding units having a tree structure according to an exemplaryembodiment.

The video encoding apparatus 100 involving video prediction based oncoding units having a tree structure includes a maximum coding unit(LCU) splitter 110, a coding unit determiner 120, and an output unit 130(e.g., an output, etc.). Hereinafter, the video encoding apparatus 100involving video prediction based on coding units having a tree structureaccording to an exemplary embodiment is referred to as a ‘video encodingapparatus 100’ for convenience of explanation.

The coding unit LCU splitter 110 may split a current picture based on anLCU that is a coding unit having a maximum size for the current pictureof an image. If the current picture is larger than the LCU, image dataof the current picture may be split into the at least one LCU. The LCUaccording to an exemplary embodiment may be a data unit having a size of32×32, 64×64, 128×128, 256×256, etc., wherein a shape of the data unitis a square having a width and length in squares of 2.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes the number of times thecoding unit is spatially split from the LCU, and as the depth increases,deeper coding units according to depths may be split from the LCU to aminimum coding unit. A depth of the LCU is an uppermost depth and adepth of the minimum coding unit is a lowermost depth. Since a size of acoding unit corresponding to each depth decreases as the depth of theLCU increases, a coding unit corresponding to an upper depth may includea plurality of coding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe LCUs according to a maximum size of the coding unit, and each of theLCUs may include deeper coding units that are split according to depths.Since the LCU according to an exemplary embodiment is split according todepths, the image data of a spatial domain included in the LCU may behierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the LCU are hierarchicallysplit, may be preset.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the LCU according to depths, anddetermines a depth to output a finally encoded image data according tothe at least one split region. In other words, the coding unitdeterminer 120 determines a coded depth by encoding the image data inthe deeper coding units according to depths, according to the LCU of thecurrent picture, and selecting a depth having the least encoding error.The determined coded depth and the encoded image data according to thedetermined coded depth are output to the output unit 130.

The image data in the LCU is encoded based on the deeper coding unitscorresponding to at least one depth equal to or below the maximum depth,and results of encoding the image data are compared based on each of thedeeper coding units. A depth having the least encoding error may beselected after comparing encoding errors of the deeper coding units. Atleast one coded depth may be selected for each LCU.

The size of the LCU is split as a coding unit is hierarchically splitaccording to depths, and the number of coding units increases. Even ifcoding units correspond to the same depth in one LCU, it is determinedwhether to split each of the coding units corresponding to the samedepth to a lower depth by measuring an encoding error of the image dataof the each coding unit, separately. Accordingly, even when image datais included in one LCU, the encoding errors may differ according toregions in the one LCU, and thus the coded depths may differ accordingto regions in the image data. Thus, one or more coded depths may bedetermined in one LCU, and the image data of the LCU may be splitaccording to coding units of at least one coded depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the LCU. The ‘coding units having atree structure’ according to an exemplary embodiment include codingunits corresponding to a depth determined to be the coded depth, fromamong all deeper coding units included in the LCU. A coding unit of acoded depth may be hierarchically determined according to depths in thesame region of the LCU, and may be independently determined in differentregions. Similarly, a coded depth in a current region may beindependently determined from a coded depth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from an LCU to a minimum coding unit. Afirst maximum depth according to an exemplary embodiment may denote thetotal number of splitting times from the LCU to the minimum coding unit.A second maximum depth according to an exemplary embodiment may denotethe total number of depth levels from the LCU to the minimum codingunit. For example, when a depth of the LCU is 0, a depth of a codingunit, in which the LCU is split once, may be set to 1, and a depth of acoding unit, in which the LCU is split twice, may be set to 2. Here, ifthe minimum coding unit is a coding unit in which the LCU is split fourtimes, 5 depth levels of depths 0, 1, 2, 3, and 4 exist, and thus thefirst maximum depth may be set to 4, and the second maximum depth may beset to 5.

Prediction encoding and transformation may be performed on the LCU. Theprediction encoding and the transformation are also performed based onthe deeper coding units according to a depth equal to or depths lessthan the maximum depth, according to the LCU.

Since the number of deeper coding units increases whenever the LCU issplit according to depths, encoding, including the prediction encodingand the transformation, has to be performed on all of the deeper codingunits generated as the depth increases. For convenience of explanation,the prediction encoding and the transformation will now be describedbased on a coding unit of a current depth, in at least one LCU.

The video encoding apparatus 100 according to an exemplary embodimentmay variously select a size or shape of a data unit for encoding theimage data. In order to encode the image data, operations, such asprediction encoding, transformation, and entropy encoding, areperformed, and at this time, the same data unit may be used for alloperations or different data units may be used for each operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the LCU, the predictionencoding may be performed based on a coding unit corresponding to acoded depth, i.e., based on a coding unit that is no longer split tocoding units corresponding to a lower depth. Hereinafter, the codingunit that is no longer split and becomes a basis unit for predictionencoding will now be referred to as a ‘prediction unit’. A partitionobtained by splitting the prediction unit may include a prediction unitor a data unit obtained by splitting at least one of a height and awidth of the prediction unit. A partition is a data unit where aprediction unit of a coding unit is split, and a prediction unit may bea partition having the same size as a coding unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split, the coding unit may become a prediction unit of2N×2N and a size of a partition may be 2N×2N, 2N×N, N×2N, or N×N.Examples of a partition type include symmetrical partitions that areobtained by symmetrically splitting a height or width of the predictionunit, partitions obtained by asymmetrically splitting the height orwidth of the prediction unit, such as 1:n or n:1, partitions that areobtained by geometrically splitting the prediction unit, and partitionshaving arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. The skip mode may be performed only on the partition of 2N×2N. Theencoding is independently performed on one prediction unit in a codingunit, thereby selecting a prediction mode having a least encoding error.

The video encoding apparatus 100 according to an exemplary embodimentmay also perform the transformation on the image data in a coding unitbased not only on the coding unit for encoding the image data, but alsobased on a data unit that is different from the coding unit. In order toperform the transformation in the coding unit, the transformation may beperformed based on a data unit having a size smaller than or equal tothe coding unit. For example, the data unit for the transformation mayinclude a data unit for an intra mode and a data unit for an inter mode.

The transformation unit in the coding unit may be recursively split intosmaller sized regions in the similar manner as the coding unit accordingto the tree structure. Thus, residual data in the coding unit may besplit according to the transformation unit according to the treestructure according to transformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is 2N×2N, may be 1 when the size of thetransformation unit is N×N, and may be 2 when the size of thetransformation unit is N/2×N/2. In other words, the transformation unitaccording to the tree structure may be set according to thetransformation depths.

Encoding information according to coding units corresponding to a codeddepth requires not only information about the coded depth, but alsoabout information related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units having a tree structure in an LCU and methods ofdetermining a prediction unit/partition, and a transformation unit,according to an exemplary embodiment, will be described in detail belowwith reference to FIGS. 10 through 20.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the LCU, which is encodedbased on the at least one coded depth determined by the coding unitdeterminer 120, and information about the coding mode according to thecoded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the coding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for oneLCU, and information about at least one coding mode is determined for acoding unit of a coded depth, information about at least one coding modemay be determined for one LCU. A coded depth of the image data of theLCU may be different according to locations since the image data ishierarchically split according to depths, and thus information about thecoded depth and the coding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and a coding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in theLCU.

The minimum unit according to an exemplary embodiment is a square dataunit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. Alternatively, the minimum unit according to anexemplary embodiment may be a maximum square data unit that may beincluded in all of the coding units, prediction units, partition units,and transformation units included in the LCU.

For example, the encoding information output by the output unit 130 maybe classified into encoding information according to deeper codingunits, and encoding information according to prediction units. Theencoding information according to the deeper coding units may includethe information about the prediction mode and about the size of thepartitions. The encoding information according to the prediction unitsmay include information about an estimated direction of an inter mode,about a reference image index of the inter mode, about a motion vector,about a chroma component of an intra mode, and about an interpolationmethod of the intra mode.

Information about a maximum size of the coding unit defined according topictures, slices, or GOPs, and information about a maximum depth may beinserted into a header of a bitstream, an SPS, or a PPS.

Information about a maximum size of the transformation unit permittedwith respect to a current video, and information about a minimum size ofthe transformation unit may also be output through a header of abitstream, an SPS, or a PPS. The output unit 130 may encode and outputreference information related to prediction, prediction information, andslice type information.

In the video encoding apparatus 100 according to a simplest exemplaryembodiment, the deeper coding unit may be a coding unit obtained bydividing a height or width of a coding unit of an upper depth, which isone layer above, by two. In other words, when the size of the codingunit of the current depth is 2N×2N, the size of the coding unit of thelower depth is N×N. The coding unit with the current depth having a sizeof 2N×2N may include a maximum of 4 of the coding units with the lowerdepth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each LCU, based on the size of the LCU andthe maximum depth determined considering characteristics of the currentpicture. Since encoding may be performed on each LCU by using any one ofvarious prediction modes and transformations, an optimum coding mode maybe determined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having a high resolution or a large data amount isencoded in a macroblock, the number of macroblocks per pictureexcessively increases. Accordingly, the number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatus 100according to an exemplary embodiment, image compression efficiency maybe increased since a coding unit is adjusted while consideringcharacteristics of an image while increasing a maximum size of a codingunit while considering a size of the image.

The video encoding apparatus 100 according to an exemplary embodimentdetermines coding units of a tree structure for every LCU, and generatessymbols as a result of encoding performed for every encoding unit. Thevideo entropy encoding apparatus 10 according to an exemplary embodimentmay perform entropy encoding on symbols for every LCU. In particular,the video entropy encoding apparatus 10 may perform entropy encoding oneach LCU according to a row of LCUs including LCUs that are seriallyarranged in a horizontal direction, for every tile or slice segmentgenerated by splitting a picture. The video entropy encoding apparatus10 may simultaneously perform parallel entropy encoding on two or morerows of LCUs.

The video entropy encoding apparatus 10 may generate a bit string ofsymbols by performing binarization on symbols that are determined byperforming encoding on LCUs. A context variable of each bin index of asyntax element value corresponding to a symbol of an LCU may bedetermined, and a bin string indicating the syntax element value may bedetermined based on the context variable of a syntax element. The videoentropy encoding apparatus 10 may adopt a bin string indicated by acurrent context variable that is determined in a context table for acurrent syntax element value.

After forming the bin string for all of syntax elements for the LCU, thevideo entropy encoding apparatus 10 may determine whether to storecontext variables that are determined in the LCU. When the syntaxelement is a last syntax element in the LCU, a dependent slice segmentmay be included in a picture in which the LCU is included, and the LCUis a last LCU in a slice segment, the context variables for the LCU maybe stored.

The context storage unit 16 may store context variables for an LCU whena dependent slice segment may be included in a picture, irrespective ofwhether a slice segment is an independent slice segment or a dependentslice segment.

When a plurality of slice segments are included in a picture, forentropy encoding for a context variable of a first LCU of a dependentslice segment that is located next to a current slice segment, a contextvariable that is stored in the current slice segment may be used.

FIG. 9 is a block diagram of a video decoding apparatus 200 based oncoding units having a tree structure according to an exemplaryembodiment.

The video decoding apparatus 200 that involves video prediction based oncoding units having a tree structure according to an exemplaryembodiment includes a receiver 210, an image data and encodinginformation extractor 220, and an image data decoder 230. Hereinafter,the video decoding apparatus 200 involving video prediction based oncoding units having a tree structure according to an exemplaryembodiment is referred to as a ‘video decoding apparatus 200’ forconvenience of explanation.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variouscoding modes, for decoding operations of the video decoding apparatus200 are identical to those described with reference to FIG. 8 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each LCU, and outputsthe extracted image data to the image data decoder 230. The image dataand encoding information extractor 220 may extract information about amaximum size of a coding unit of a current picture, from a header aboutthe current picture, an SPS, or a PPS.

The image data and encoding information extractor 220 extractsinformation about a coded depth and a coding mode for the coding unitshaving a tree structure according to each LCU, from the parsedbitstream. The extracted information about the coded depth and thecoding mode is output to the image data decoder 230. In other words, theimage data in a bit string is split into the LCU so that the image datadecoder 230 decodes the image data for each LCU.

The information about the coded depth and the coding mode according tothe LCU may be set for information about at least one coding unitcorresponding to the coded depth, and information about a coding modemay include information about a partition type of a corresponding codingunit corresponding to the coded depth, about a prediction mode, and asize of a transformation unit. Splitting information according to depthsmay be extracted as the information about the coded depth.

The information about the coded depth and the coding mode according toeach LCU extracted by the image data and encoding information extractor220 is information about a coded depth and a coding mode determined togenerate a minimum encoding error when an encoder, such as the videoencoding apparatus 100, repeatedly performs encoding for each deepercoding unit according to depths according to each LCU. Accordingly, thevideo decoding apparatus 200 may restore an image by decoding the imagedata according to a coded depth and a coding mode that generates theminimum encoding error.

Since encoding information about the coded depth and the coding mode maybe assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the coding mode according to the predetermined dataunits. If information about a coded depth and coding mode of acorresponding LCU is recorded according to predetermined data units, thepredetermined data units to which the same information about the codeddepth and the coding mode is assigned may be inferred to be the dataunits included in the same LCU.

The image data decoder 230 restores the current picture by decoding theimage data in each LCU based on the information about the coded depthand the coding mode according to the LCUs. In other words, the imagedata decoder 230 may decode the encoded image data based on theextracted information about the partition type, the prediction mode, andthe transformation unit for each coding unit from among the coding unitshaving the tree structure included in each LCU. A decoding process mayinclude a prediction including intra prediction and motion compensation,and an inverse transformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

In addition, the image data decoder 230 may read information about atransformation unit according to a tree structure for each coding unitso as to perform inverse transformation based on transformation unitsfor each coding unit, for inverse transformation for each LCU. Throughthe inverse transformation, a pixel value of a spatial domain of thecoding unit may be restored.

The image data decoder 230 may determine a coded depth of a current LCUby using split information according to depths. If the split informationindicates that image data is no longer split in the current depth, thecurrent depth is a coded depth. Accordingly, the image data decoder 230may decode encoded data in the current LCU by using the informationabout the partition type of the prediction unit, the prediction mode,and the size of the transformation unit for each coding unitcorresponding to the coded depth.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same coding mode. As such, the currentcoding unit may be decoded by obtaining the information about the codingmode for each coding unit.

The receiver 210 may include the video entropy decoding apparatus 20 ofFIG. 2A. The video entropy decoding apparatus 20 may parse a pluralityof rows of LCUs from a received bitstream.

When the receiver 22 extracts a first row of LCUs and a second row ofLCUs from the bitstream, the first entropy decoder 24 may sequentiallyrestore symbols of LCUs of the first row of LCUs by performing entropydecoding on the first row of LCUs.

The video entropy decoding apparatus 20 may determine a bin string and abin index for an LCU that is obtained from the bitstream. The videoentropy decoding apparatus 20 may store data about a context tablecontaining a correlation between a bin string and a context variable foreach syntax element. The video entropy decoding apparatus 20 maydetermine a value of a syntax element indicated by a current bin stringby comparing bin strings that may be assigned to the syntax element in acurrent context variable based on the context table with the bin stringin the bin index that is currently determined.

When the syntax element is a last syntax element in the LCU, A dependentslice segment may be included in a picture in which the LCU is included,and the LCU is a last LCU in a slice segment, the video entropy decodingapparatus 20 may store context variables for the LCU. When a dependentslice segment may be included in a picture irrespective of whether aslice segment is an independent slice segment or the dependent slicesegment, context variables for the LCU may be stored.

When a plurality of slice segments are included in a picture, forentropy encoding for a context variable of a first LCU of a dependentslice segment that is located next to a current slice segment, a contextvariable that is stored in the current slice segment may be used.

The video entropy decoding apparatus 20 may restore symbols of the LCUby using a value of each syntax element.

As a result, the video decoding apparatus 200 may obtain informationabout a coding unit having a minimum encoding error by recursivelyperforming encoding on each LCU during an encoding process and may usethe information to decode a current picture. That is, encoded image dataof coding units having a tree structure determined as optimum codingunits for each LCU may be decoded.

Accordingly, even when an image has a high resolution or a large dataamount, image data may be efficiently decoded and restored according toa coding mode and a size of a coding unit that are adaptively determinedaccording to characteristics of the image by using information about anoptimum coding mode that is transmitted from an encoder

FIG. 10 is a diagram for explaining a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed by width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 10 denotes a total number of splits from an LCU to a minimumdecoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havinga higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe vide data 310 may include an LCU having a long axis size of 64, andcoding units having long axis sizes of 32 and 16 since depths areincreased to two layers by splitting the LCU twice. Since the maximumdepth of the video data 330 is 1, coding units 335 of the video data 330may include an LCU having a long axis size of 16, and coding unitshaving a long axis size of 8 since depths are increased to one layer bysplitting the LCU once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include an LCU having a long axis size of 64, andcoding units having long axis sizes of 32, 16, and 8 since the depthsare increased to 3 layers by splitting the LCU three times. As a depthincreases, detailed information may be precisely expressed.

FIG. 11 is a block diagram of an image encoder 400 based on coding unitsaccording to an exemplary embodiment.

The image encoder 400 according to an exemplary embodiment performsoperations of the coding unit determiner 120 of the video encodingapparatus 100 to encode image data. In other words, an intra predictor410 performs intra prediction on coding units in an intra mode, fromamong a current frame 405, and a motion estimator 420 and a motioncompensator 425 respectively perform inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformcoefficient through a transformer 430 and a quantizer 440. The quantizedtransform coefficient is restored as data in a spatial domain through aninverse quantizer 460 and an inverse transformer 470, and the restoreddata in the spatial domain is output as the reference frame 495 afterbeing post-processed through a deblocking unit 480 (e.g., a deblockingfilter, etc.) and a loop filtering unit 490 (e.g., a loop filter, anoffset adjusting unit, an offset adjuster, etc.). The quantizedtransform coefficient may be output as a bitstream 455 through anentropy encoder 450.

In order for the image encoder 400 to be applied to the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 have to perform operations based on eachcoding unit among coding units having a tree structure while consideringthe maximum depth of each LCU.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determine partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentLCU, and the transformer 430 determines the size of the transformationunit in each coding unit from among the coding units having a treestructure.

In particular, the entropy encoder 450 may correspond to the videoentropy encoding apparatus 10 according to an exemplary embodiment.

FIG. 12 is a block diagram of an image decoder 500 based on coding unitsaccording to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding required for decoding from a bitstream 505. The encodedimage data is output as inverse quantized data through an entropydecoder 520 and an inverse quantizer 530, and the inverse quantized datais restored to image data in a spatial domain through an inversetransformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 (e.g., a deblocking filter, etc.) and a loop filtering unit 580(e.g., an offset adjusting unit, an offset adjuster, a loop filter,etc.). The image data that is post-processed through the deblocking unit570 and the loop filtering unit 580 may be output as the reference frame585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied to the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 have to performoperations based on coding units having a tree structure for each LCU.

Specifically, the intra prediction 550 and the motion compensator 560determine partitions and a prediction mode for each of the coding unitshaving a tree structure, and the inverse transformer 540 determines asize of a transformation unit for each coding unit. In particular, theentropy decoder 520 may correspond to the video entropy decodingapparatus 20 according to an exemplary embodiment.

FIG. 13 is a diagram illustrating deeper coding units according todepths and partitions according to an exemplary embodiment.

The video encoding apparatus 100 according to an exemplary embodimentand the video decoding apparatus 200 according to an exemplaryembodiment use hierarchical coding units so as to considercharacteristics of an image. A maximum height, a maximum width, and amaximum depth of coding units may be adaptively determined according tothe characteristics of the image, or may be differently set by a user.Sizes of deeper coding units according to depths may be determinedaccording to the predetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 4. In this case, themaximum depth refers to a total number of times the coding unit is splitfrom the LCU to the minimum coding unit. Since a depth increases along avertical axis of the hierarchical structure 600, a height and a width ofthe deeper coding unit are each split. A prediction unit and partitions,which are bases for prediction encoding of each deeper coding unit, areshown along a horizontal axis of the hierarchical structure 600.

In other words, a coding unit 610 is an LCU in the hierarchicalstructure 600, wherein a depth is 0 and a size, i.e., a height by width,is 64×64. The depth increases along the vertical axis, and a coding unit620 having a size of 32×32 and a depth of 1, a coding unit 630 having asize of 16×16 and a depth of 2, a coding unit 640 having a size of 8×8and a depth of 3, and a coding unit 650 having a size of 4×4 and a depthof 4. The coding unit 640 having a size of 4×4 and a depth of 4 is aminimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having a size of 64×64 and a depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

Lastly, the coding unit 650 having a depth of 4 and a size of 4×4 thatis a minimum coding unit is a coding unit having a lowermost depth, anda corresponding prediction unit may be set to only partitions having asize of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the LCU 610, the coding unit determiner 120 of the videoencoding apparatus 100 according to an exemplary embodiment has toperform encoding for coding units corresponding to each depth includedin the LCU 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth increases. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 have to be eachencoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth increasesalong the vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 14 is a diagram for explaining a relationship between a coding unit710 and transformation units 720 according to an exemplary embodiment.

The video encoding apparatus 100 according to an exemplary embodiment orthe video decoding apparatus 200 according to an exemplary embodimentencodes or decodes an image according to coding units having sizessmaller than or equal to an LCU for each LCU. Sizes of transformationunits for transformation during encoding may be selected based on dataunits that are not larger than a corresponding coding unit.

For example, in the video encoding apparatus 100 according to anexemplary embodiment or the video decoding apparatus 200 according to anexemplary embodiment, if a size of the coding unit 710 is 64×64,transformation may be performed by using the transformation units 720having a size of 32×32.

Data of the coding unit 710 having the size of 64×64 may be encoded byperforming the transformation on each of the transformation units havingthe size of 32×32, 16×16, 8×8, and 4×4, which are smaller than 64×64,and then a transformation unit having the least coding error may beselected.

FIG. 15 is a diagram for explaining encoding information of coding unitscorresponding to a coded depth according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 according to anexemplary embodiment may encode and transmit information 800 about apartition type, information 810 about a prediction mode, and information820 about a size of a transformation unit for each coding unitcorresponding to a coded depth, as information about a coding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about a partition type is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N.

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 210 of the videodecoding apparatus 200 according to an exemplary embodiment may extractand use the information 800, 810, and 820 for decoding, according toeach deeper coding unit.

FIG. 16 is a diagram illustrating deeper coding units according todepths according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, a partition type 916 having a size of N_0×2N_0, and apartition type 918 having a size of N_0×N_0. FIG. 16 only illustratesthe partition types 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition type is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition type. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition type 918, a depthis changed from 0 to 1 to split the partition type 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, a partition type 946 having a size ofN_1×2N_1, and a partition type 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition type 948, a depthis changed from 1 to 2 to split the partition type 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and split information maybe encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition type 992 having a size of 2N_(d−1)×2N_(d−1), a partition type994 having a size of 2N_(d−1)×N_(d−1), a partition type 996 having asize of N_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitiontypes 992 through 998 to search for a partition type having a minimumencoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current LCU 900 is determined to be d−1 and a partitiontype of the current LCU 900 may be determined to be N_(d−1)×N_(d−1).Since the maximum depth is d and a minimum coding unit 980 having alowermost depth of d−1 is no longer split to a lower depth, splitinformation for the minimum coding unit 980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current LCU. A minimumunit according to an exemplary embodiment may be a square data unitobtained by splitting a minimum coding unit 980 by 4. By performing theencoding repeatedly, the video encoding apparatus 100 according to anexemplary embodiment may select a depth having the least encoding errorby comparing encoding errors according to depths of the coding unit 900to determine a coded depth, and set a corresponding partition type and aprediction mode as a coding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about a coding mode. Since a coding unit issplit from a depth of 0 to a coded depth, only split information of thecoded depth is set to 0, and split information of depths excluding thecoded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 according to an exemplary embodiment may extractand use the information about the coded depth and the prediction unit ofthe coding unit 900 to decode the partition 912. The video decodingapparatus 200 according to an exemplary embodiment may determine adepth, in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about a coding modeof the corresponding depth for decoding.

FIGS. 17 through 19 are diagrams for explaining a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100 according to an exemplary embodiment, in an LCU. The predictionunits 1060 are partitions of prediction units of each of the codingunits 1010, and the transformation units 1070 are transformation unitsof each of the coding units 1010.

When a depth of an LCU is 0 in the coding units 1010, depths of codingunits 1012 and 1054 are 1, depths of coding units 1014, 1016, 1018,1028, 1050, and 1052 are 2, depths of coding units 1020, 1022, 1024,1026, 1030, 1032, and 1048 are 3, and depths of coding units 1040, 1042,1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition types in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitiontypes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition type of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. The coding units 1014, 1016,1022, 1032, 1048, 1050, 1052, and 1054 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding apparatus 100 accordingto an exemplary embodiment and the video decoding apparatus 200according to an exemplary embodiment may perform intra prediction,motion estimation, motion compensation, transformation, and inversetransformation individually on a data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of an LCU to determine anoptimum coding unit, and thus coding units having a recursive treestructure may be obtained. Encoding information may include splitinformation about a coding unit, information about a partition type,information about a prediction mode, and information about a size of atransformation unit. Table 1 shows the encoding information that may beset by the video encoding apparatus 100 according to an exemplaryembodiment and the video decoding apparatus 200 according to anexemplary embodiment.

TABLE 1 Split Information 0 (Encoding on Coding Unit having Size of 2N ×2N and Current Depth of d) Size of Transformation Unit Split SplitPartition Type Information 0 Information 1 Symmetrical Asymmetrical ofof Prediction Partition Partition Transformation Transformation SplitMode Type Type Unit Unit Information 1 Intra 2N × 2N 2N × nU 2N × 2N N ×N Repeatedly Inter 2N × N 2N × nD (Symmetrical Encode Skip  N × 2N nL ×2N Type) Coding Units (Only  N × N nR × 2N N/2 × N/2 having Lower 2N ×2N) (Asymmetrical Depth of d + 1 Type)

The output unit 130 of the video encoding apparatus 100 according to anexemplary embodiment may output the encoding information about thecoding units having a tree structure, and the image data and encodinginformation extractor 220 of the video decoding apparatus 200 accordingto an exemplary embodiment may extract the encoding information aboutthe coding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Further, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structureaccording to an exemplary embodiment may include at least one of acoding unit corresponding to a coded depth, a prediction unit, and aminimum unit. The coding unit corresponding to the coded depth mayinclude at least one of a prediction unit and a minimum unit containingthe same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. A corresponding codingunit corresponding to a coded depth is determined by using encodinginformation of a data unit, and thus a distribution of coded depths inan LCU may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 20 is a diagram for explaining a relationship between a codingunit, a prediction unit, and a transformation unit according to codingmode information of Table 1.

An LCU 1300 includes coding units 1302, 1304, 1306, 1312, 1314, 1316,and 1318 of coded depths. Here, since the coding unit 1318 is a codingunit of a coded depth, split information may be set to 0. Informationabout a partition type of the coding unit 1318 having a size of 2N×2Nmay be set to be one of a partition type 1322 having a size of 2N×2N, apartition type 1324 having a size of 2N×N, a partition type 1326 havinga size of N×2N, a partition type 1328 having a size of N×N, a partitiontype 1332 having a size of 2N×nU, a partition type 1334 having a size of2N×nD, a partition type 1336 having a size of nL×2N, and a partitiontype 1338 having a size of nR×2N.

Split information (TU size flag) of a transformation unit is a type of atransformation index. The size of the transformation unit correspondingto the transformation index may be changed according to a predictionunit type or a partition type of the coding unit.

For example, when the partition type is set to be symmetrical, i.e. thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if a TU size flag of a transformation unitis 0, and a transformation unit 1344 having a size of N×N is set if a TUsize flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 20, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. Split information (TU size flag) of atransformation unit may be an example of a transformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an exemplary embodiment, together with a maximum size andminimum size of the transformation unit. The video encoding apparatus100 according to an exemplary embodiment is capable of encoding maximumtransformation unit size information, minimum transformation unit sizeinformation, and a maximum TU size flag. The result of encoding themaximum transformation unit size information, the minimum transformationunit size information, and the maximum TU size flag may be inserted intoan SPS. The video decoding apparatus 200 according to an exemplaryembodiment may decode video by using the maximum transformation unitsize information, the minimum transformation unit size information, andthe maximum TU size flag.

For example, (a) if the size of a current coding unit is 64×64 and amaximum transformation unit size is 32×32, (a−1) then the size of atransformation unit may be 32×32 when a TU size flag is 0, (a−2) may be16×16 when the TU size flag is 1, and (a−3) may be 8×8 when the TU sizeflag is 2.

As another example, (b) if the size of the current coding unit is 32×32and a minimum transformation unit size is 32×32, (b−1) then the size ofthe transformation unit may be 32×32 when the TU size flag is 0. Here,the TU size flag cannot be set to a value other than 0, since the sizeof the transformation unit cannot be less than 32×32.

As another example, (c) if the size of the current coding unit is 64×64and a maximum TU size flag is 1, then the TU size flag may be 0 or 1.Here, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):CurrMinTuSize=max(MinTransformSize,RootTuSize/(2^MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2^MaxTransformSizeIndex)’ denotes a transformationunit size when the transformation unit size ‘RootTuSize’, when the TUsize flag is 0, is split a number of times corresponding to the maximumTU size flag, and ‘MinTransformSize’ denotes a minimum transformationsize. Thus, a smaller value from among‘RootTuSize/(2^MaxTransformSizeIndex)’ and ‘MinTransformSize’ may be thecurrent minimum transformation unit size ‘CurrMinTuSize’ that can bedetermined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.RootTuSize=min(MaxTransformSize,PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’, when the TU size flag is 0, maybe a smaller value from among the maximum transformation unit size andthe current prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.RootTuSize=min(MaxTransformSize,PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and an exemplary embodiment is not limited thereto.

According to the video encoding method based on coding units having atree structure as described with reference to FIGS. 8 through 20, imagedata of a spatial domain is encoded for each of coding units having atree structure. According to the video decoding method based on codingunits having a tree structure, decoding is performed for each LCU torestore image data of a spatial domain. Thus, a picture and a video thatis a picture sequence may be restored. The restored video may bereproduced by a reproducing apparatus, stored in a storage medium, ortransmitted through a network.

The exemplary embodiments may be written as computer programs and may beimplemented in general-use digital computers that execute the programsusing a computer-readable recording medium. Examples of thecomputer-readable recording medium include magnetic storage media (e.g.,ROM, floppy discs, hard discs, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs).

For convenience of explanation, the video encoding method involving theentropy encoding method described with reference to FIGS. 1A through 20,will be collectively referred to as a ‘video encoding method accordingto an exemplary embodiment’. In addition, the video decoding methodinvolving the entropy decoding method described with reference to FIGS.1A through 20, will be collectively referred to as a ‘video decodingmethod according to an exemplary embodiment’.

The video encoding apparatus 100 including the entropy encodingapparatus 10 and a video encoding apparatus including the image encoder400 described with reference to FIGS. 1A through 20 will be referred toas a ‘video encoding apparatus according to an exemplary embodiment’. Inaddition, the video decoding apparatus 200 including the entropydecoding apparatus 20 and the image decoder 500 been descried withreference to FIGS. 1A through 20 will be referred to as a ‘videodecoding apparatus according to an exemplary embodiment’.

A computer-readable recording medium storing a program, e.g., a disc26000, according to an exemplary embodiment will now be described indetail.

FIG. 21 is a diagram illustrating a physical structure of the disc 26000in which a program is stored according to an exemplary embodiment. Thedisc 26000, which is a storage medium, may be a hard drive, a compactdisc-read only memory (CD-ROM) disc, a Blu-ray disc, or a digitalversatile disc (DVD). The disc 26000 includes a plurality of concentrictracks Tr that are each divided into a specific number of sectors Se ina circumferential direction of the disc 26000. In a specific region ofthe disc 26000, a program that executes the quantization parameterdetermination method, the video encoding method and the video decodingmethod described above may be assigned and stored.

A computer system embodied using a storage medium that stores a programfor executing the video encoding method and the video decoding method asdescribed above will now be described with reference to FIG. 22.

FIG. 22 is a diagram illustrating a disc drive 26800 for recording andreading a program by using the disc 26000. A computer system 27000 maystore a program that executes at least one of a video encoding methodand a video decoding method according to an exemplary embodiment, in thedisc 26000 via the disc drive 26800. To run the program stored in thedisc 26000 in the computer system 27000, the program may be read fromthe disc 26000 and be transmitted to the computer system 26700 by usingthe disc drive 26800.

The program that executes at least one of a video encoding method and avideo decoding method according to an exemplary embodiment may be storednot only in the disc 26000 illustrated in FIG. 21 or 22 but also in amemory card, a ROM cassette, or a solid state drive (SSD).

A system to which the video encoding method and a video decoding methoddescribed above are applied will be described below.

FIG. 23 is a diagram illustrating an overall structure of a contentsupply system 11000 for providing a content distribution service. Aservice area of a communication system is divided intopredetermined-sized cells, and wireless base stations 11700, 11800,11900, and 12000 are installed in these cells, respectively.

The content supply system 11000 includes a plurality of independentdevices. For example, the plurality of independent devices, such as acomputer 12100, a personal digital assistant (PDA) 12200, a video camera12300, and a mobile phone 12500, are connected to the Internet 11100 viaan internet service provider 11200, a communication network 11400, andthe wireless base stations 11700, 11800, 11900, and 12000.

However, the content supply system 11000 is not limited to asillustrated in FIG. 24, and devices may be selectively connectedthereto. The plurality of independent devices may be directly connectedto the communication network 11400, not via the wireless base stations11700, 11800, 11900, and 12000.

The video camera 12300 is an imaging device, e.g., a digital videocamera, which is capable of capturing video images. The mobile phone12500 may employ at least one communication method from among variousprotocols, e.g., Personal Digital Communications (PDC), Code DivisionMultiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA),Global System for Mobile Communications (GSM), and Personal HandyphoneSystem (PHS).

The video camera 12300 may be connected to a streaming server 11300 viathe wireless base station 11900 and the communication network 11400. Thestreaming server 11300 allows content received from a user via the videocamera 12300 to be streamed via a real-time broadcast. The contentreceived from the video camera 12300 may be encoded using the videocamera 12300 or the streaming server 11300. Video data captured by thevideo camera 12300 may be transmitted to the streaming server 11300 viathe computer 12100.

Video data captured by a camera 12600 may also be transmitted to thestreaming server 11300 via the computer 12100. The camera 12600 is animaging device capable of capturing both still images and video images,similar to a digital camera. The video data captured by the camera 12600may be encoded using the camera 12600 or the computer 12100. Softwarethat performs encoding and decoding video may be stored in acomputer-readable recording medium, e.g., a CD-ROM disc, a floppy disc,a hard disc drive, an SSD, or a memory card, which may be accessible bythe computer 12100.

If video data is captured by a camera built in the mobile phone 12500,the video data may be received from the mobile phone 12500.

The video data may also be encoded by a large scale integrated circuit(LSI) system installed in the video camera 12300, the mobile phone12500, or the camera 12600.

The content supply system 11000 may encode content data recorded by auser using the video camera 12300, the camera 12600, the mobile phone12500, or another imaging device, e.g., content recorded during aconcert, and transmit the encoded content data to the streaming server11300. The streaming server 11300 may transmit the encoded content datain a type of a streaming content to other clients that request thecontent data.

The clients are devices capable of decoding the encoded content data,e.g., the computer 12100, the PDA 12200, the video camera 12300, or themobile phone 12500. Thus, the content supply system 11000 allows theclients to receive and reproduce the encoded content data. The contentsupply system 11000 allows the clients to receive the encoded contentdata and decode and reproduce the encoded content data in real time,thereby enabling personal broadcasting.

Encoding and decoding operations of the plurality of independent devicesincluded in the content supply system 11000 may be similar to those of avideo encoding apparatus and a video decoding apparatus according to anexemplary embodiment.

The mobile phone 12500 included in the content supply system 11000according to an exemplary embodiment will now be described in greaterdetail with reference to FIGS. 24 and 25.

FIG. 24 is a diagram illustrating an external structure of the mobilephone 12500 to which a video encoding method and a video decoding methodaccording to an exemplary embodiment are applied according to anexemplary embodiment. The mobile phone 12500 may be a smart phone, thefunctions of which are not limited and a large number of the functionsof which may be changed or expanded.

The mobile phone 12500 includes an internal antenna 12510 via which aradio-frequency (RF) signal may be exchanged with the wireless basestation 12000, and includes a display screen 12520 for displaying imagescaptured by a camera 12530 or images that are received via the antenna12510 and decoded, e.g., a liquid crystal display (LCD) or an organiclight-emitting diode (OLED) screen. The mobile phone 12500 includes anoperation panel 12540 including a control button and a touch panel. Ifthe display screen 12520 is a touch screen, the operation panel 12540further includes a touch sensing panel of the display screen 12520. Themobile phone 12500 includes a speaker 12580 for outputting voice andsound or another type of sound output unit, and a microphone 12550 forinputting voice and sound or another type sound input unit. The mobilephone 12500 further includes the camera 12530, such as a charge-coupleddevice (CCD) camera, to capture video and still images. The mobile phone12500 may further include a storage medium 12570 for storingencoded/decoded data, e.g., video or still images captured by the camera12530, received via email, or obtained according to various ways; and aslot 12560 via which the storage medium 12570 is loaded into the mobilephone 12500. The storage medium 12570 may be a flash memory, e.g., asecure digital (SD) card or an electrically erasable and programmableread only memory (EEPROM) included in a plastic case.

FIG. 25 is a diagram illustrating an internal structure of the mobilephone 12500. To systemically control parts of the mobile phone 12500including the display screen 12520 and the operation panel 12540, apower supply circuit 12700, an operation input controller 12640, animage encoding unit 12720, a camera interface 12630, an LCD controller12620, an image decoding unit 12690, a multiplexer/demultiplexer 12680,a recording/reading unit 12670, a modulation/demodulation unit 12660,and a sound processor 12650 are connected to a central controller 12710via a synchronization bus 12730.

If a user operates a power button and sets from a ‘power off’ state to a‘power on’ state, the power supply circuit 12700 supplies power to allthe parts of the mobile phone 12500 from a battery pack, thereby settingthe mobile phone 12500 in an operation mode.

The central controller 12710 includes a central processing unit (CPU), aROM, and a RAM.

While the mobile phone 12500 transmits communication data to theoutside, a digital signal is generated by the mobile phone 12500 undercontrol of the central controller 12710. For example, the soundprocessor 12650 may generate a digital sound signal, the image encodingunit 12720 may generate a digital image signal, and text data of amessage may be generated via the operation panel 12540 and the operationinput controller 12640. When a digital signal is transmitted to themodulation/demodulation unit 12660 under control of the centralcontroller 12710, the modulation/demodulation unit 12660 modulates afrequency band of the digital signal, and a communication circuit 12610performs digital-to-analog conversion (DAC) and frequency conversion onthe frequency band-modulated digital sound signal. A transmission signaloutput from the communication circuit 12610 may be transmitted to avoice communication base station or the wireless base station 12000 viathe antenna 12510.

For example, when the mobile phone 12500 is in a conversation mode, asound signal obtained via the microphone 12550 is transformed into adigital sound signal by the sound processor 12650, under control of thecentral controller 12710. The digital sound signal may be transformedinto a transformation signal via the modulation/demodulation unit 12660and the communication circuit 12610, and may be transmitted via theantenna 12510.

When a text message, e.g., email, is transmitted in a data communicationmode, text data of the text message is input via the operation panel12540 and is transmitted to the central controller 12610 via theoperation input controller 12640. Under control of the centralcontroller 12610, the text data is transformed into a transmissionsignal via the modulation/demodulation unit 12660 and the communicationcircuit 12610 and is transmitted to the wireless base station 12000 viathe antenna 12510.

To transmit image data in the data communication mode, image datacaptured by the camera 12530 is provided to the image encoding unit12720 via the camera interface 12630. The captured image data may bedirectly displayed on the display screen 12520 via the camera interface12630 and the LCD controller 12620.

A structure of the image encoding unit 12720 may correspond to that ofthe video encoding apparatus 100 described above. The image encodingunit 12720 may transform the image data received from the camera 12530into compressed and encoded image data according to a video encodingmethod employed by the video encoding apparatus 100 or the image encoder400 described above, and then output the encoded image data to themultiplexer/demultiplexer 12680. During a recording operation of thecamera 12530, a sound signal obtained by the microphone 12550 of themobile phone 12500 may be transformed into digital sound data via thesound processor 12650, and the digital sound data may be transmitted tothe multiplexer/demultiplexer 12680.

The multiplexer/demultiplexer 12680 multiplexes the encoded image datareceived from the image encoding unit 12720, together with the sounddata received from the sound processor 12650. A result of multiplexingthe data may be transformed into a transmission signal via themodulation/demodulation unit 12660 and the communication circuit 12610,and may then be transmitted via the antenna 12510.

While the mobile phone 12500 receives communication data from theoutside, frequency recovery and ADC are performed on a signal receivedvia the antenna 12510 to transform the signal into a digital signal. Themodulation/demodulation unit 12660 modulates a frequency band of thedigital signal. The frequency-band modulated digital signal istransmitted to the video decoding unit 12690, the sound processor 12650,or the LCD controller 12620, according to the type of the digitalsignal.

In the conversation mode, the mobile phone 12500 amplifies a signalreceived via the antenna 12510, and obtains a digital sound signal byperforming frequency conversion and ADC on the amplified signal. Areceived digital sound signal is transformed into an analog sound signalvia the modulation/demodulation unit 12660 and the sound processor12650, and the analog sound signal is output via the speaker 12580,under control of the central controller 12710.

When in the data communication mode, data of a video file accessed at anInternet website is received, a signal received from the wireless basestation 12000 via the antenna 12510 is output as multiplexed data viathe modulation/demodulation unit 12660, and the multiplexed data istransmitted to the multiplexer/demultiplexer 12680.

To decode the multiplexed data received via the antenna 12510, themultiplexer/demultiplexer 12680 demultiplexes the multiplexed data intoan encoded video data stream and an encoded audio data stream. Via thesynchronization bus 12730, the encoded video data stream and the encodedaudio data stream are provided to the video decoding unit 12690 and thesound processor 12650, respectively.

A structure of the image decoding unit 12690 may correspond to that ofthe video decoding apparatus according to an exemplary embodiment. Theimage decoding unit 12690 may decode the encoded video data to obtainrestored video data and provide the restored video data to the displayscreen 1252 via the LCD controller 1262 according to the video decodingmethod according to an exemplary embodiment.

Thus, the data of the video file accessed at the Internet website may bedisplayed on the display screen 1252. At the same time, the soundprocessor 1265 may transform audio data into an analog sound signal, andprovide the analog sound signal to the speaker 1258. Thus, audio datacontained in the video file accessed at the Internet website may also bereproduced via the speaker 1258.

The mobile phone 1250 or another type of communication terminal may be atransceiving terminal including both a video encoding apparatus and avideo decoding apparatus according to an exemplary embodiment, may be atransceiving terminal including only the video encoding apparatusaccording to an exemplary embodiment, or may be a transceiving terminalincluding only the video decoding apparatus according to an exemplaryembodiment.

A communication system according to an exemplary embodiment is notlimited to the communication system described above with reference toFIG. 24. For example, FIG. 26 is a diagram illustrating a digitalbroadcasting system employing a communication system according to anexemplary embodiment. The digital broadcasting system of FIG. 26 mayreceive a digital broadcast transmitted via a satellite or a terrestrialnetwork by using a video encoding apparatus and a video decodingapparatus according to an exemplary embodiment.

Specifically, a broadcasting station 12890 transmits a video data streamto a communication satellite or a broadcasting satellite 12900 by usingradio waves. The broadcasting satellite 12900 transmits a broadcastsignal, and the broadcast signal is transmitted to a satellite broadcastreceiver via a household antenna 12860. In every house, an encoded videostream may be decoded and reproduced by a TV receiver 12810, a set-topbox 12870, or another device.

When a video decoding apparatus according to an exemplary embodiment isimplemented in a reproducing apparatus 12830, the reproducing apparatus12830 may parse and decode an encoded video stream recorded on a storagemedium 12820, such as a disc or a memory card to restore digitalsignals. Thus, the restored video signal may be reproduced, for example,on a monitor 12840.

In the set-top box 12870 connected to the antenna 12860 for asatellite/terrestrial broadcast or a cable antenna 12850 for receiving acable television (TV) broadcast, a video decoding apparatus according toan exemplary embodiment may be installed. Data output from the set-topbox 12870 may also be reproduced on a TV monitor 12880.

As another example, a video decoding apparatus according to an exemplaryembodiment may be installed in the TV receiver 12810 instead of theset-top box 12870.

An automobile 12920 that has an appropriate antenna 12910 may receive asignal transmitted from the satellite 12900 or the wireless base station11700. A decoded video may be reproduced on a display screen of anautomobile navigation system 12930 installed in the automobile 12920.

A video signal may be encoded by a video encoding apparatus according toan exemplary embodiment and may then be stored in a storage medium.Specifically, an image signal may be stored in a DVD disc 12960 by a DVDrecorder or may be stored in a hard disc by a hard disc recorder 12950.As another example, the video signal may be stored in an SD card 12970.If the hard disc recorder 12950 includes a video decoding apparatusaccording to an exemplary embodiment, a video signal recorded on the DVDdisc 12960, the SD card 12970, or another storage medium may bereproduced on the TV monitor 12880.

The automobile navigation system 12930 may not include the camera 12530,the camera interface 12630, and the image encoding unit 12720 of FIG.26. For example, the computer 12100 and the TV receiver 12810 may not beincluded in the camera 12530, the camera interface 12630, and the imageencoding unit 12720 of FIG. 26.

FIG. 27 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus according to an exemplary embodiment.

The cloud computing system may include a cloud computing server 14100, auser database (DB) 14100, a plurality of computing resources 14200, anda user terminal.

The cloud computing system provides an on-demand outsourcing service ofthe plurality of computing resources 14200 via a data communicationnetwork, e.g., the Internet, in response to a request from the userterminal. Under a cloud computing environment, a service providerprovides users with desired services by combining computing resources atdata centers located at physically different locations by usingvirtualization technology. A service user does not have to installcomputing resources, e.g., an application, a storage, an operatingsystem (OS), and security, into his/her own terminal in order to usethem, but may select and use desired services from among services in avirtual space generated through the virtualization technology, at adesired point in time.

A user terminal of a specified service user is connected to the cloudcomputing server 14100 via a data communication network including theInternet and a mobile telecommunication network. User terminals may beprovided cloud computing services, and particularly video reproductionservices, from the cloud computing server 14100. The user terminals maybe various types of electronic devices capable of being connected to theInternet, e.g., a desktop PC 14300, a smart TV 14400, a smart phone14500, a notebook computer 14600, a portable multimedia player (PMP)14700, a tablet PC 14800, and the like.

The cloud computing server 14100 may combine the plurality of computingresources 14200 distributed in a cloud network and provide userterminals with a result of combining. The plurality of computingresources 14200 may include various data services, and may include datauploaded from user terminals. As described above, the cloud computingserver 14100 may provide user terminals with desired services bycombining video database distributed in different regions according tothe virtualization technology.

User information about users who have subscribed for a cloud computingservice is stored in the user DB 14100. The user information may includelogging information, addresses, names, and personal credit informationof the users. The user information may further include indexes ofvideos. Here, the indexes may include a list of videos that have alreadybeen reproduced, a list of videos that are being reproduced, a pausingpoint of a video that was being reproduced, and the like.

Information about a video stored in the user DB 14100 may be sharedbetween user devices. For example, when a video service is provided tothe notebook computer 14600 in response to a request from the notebookcomputer 14600, a reproduction history of the video service is stored inthe user DB 14100. When a request to reproduce this video service isreceived from the smart phone 14500, the cloud computing server 14000searches for and reproduces this video service, based on the user DB14100. When the smart phone 14500 receives a video data stream from thecloud computing server 14100, a process of reproducing video by decodingthe video data stream is similar to an operation of the mobile phone12500 described above with reference to FIG. 24.

The cloud computing server 14100 may refer to a reproduction history ofa desired video service, stored in the user DB 14100. For example, thecloud computing server 14100 receives a request to reproduce a videostored in the user DB 14100, from a user terminal. If this video wasbeing reproduced, then a method of streaming this video, performed bythe cloud computing server 14100, may vary according to the request fromthe user terminal, i.e., according to whether the video will bereproduced, starting from a start thereof or a pausing point thereof.For example, if the user terminal requests to reproduce the video,starting from the start thereof, the cloud computing server 14100transmits streaming data of the video starting from a first framethereof to the user terminal. If the user terminal requests to reproducethe video, starting from the pausing point thereof, the cloud computingserver 14100 transmits streaming data of the video starting from a framecorresponding to the pausing point, to the user terminal.

In this case, the user terminal may include a video decoding apparatusas described above with reference to FIGS. 1A to 20. As another example,the user terminal may include a video encoding apparatus as describedabove with reference to FIGS. 1A to 20. Alternatively, the user terminalmay include both the video decoding apparatus and the video encodingapparatus as described above with reference to FIGS. 1A to 20.

Various applications of a video encoding method, a video decodingmethod, a video encoding apparatus, and a video decoding apparatusaccording to an exemplary embodiment described above with reference toFIGS. 1A to 20 have been described above with reference to FIGS. 21 to27. However, methods of storing the video encoding method and the videodecoding method in a storage medium or methods of implementing the videoencoding apparatus and the video decoding apparatus in a device,according to various exemplary embodiments, are not limited to theembodiments described above with reference to FIGS. 21 to 27.

While exemplary embodiments have been particularly shown and describedwith reference to the drawings by using specific terms, the exemplaryembodiments and terms have merely been used for explanation and shouldnot be construed as limiting the scope of the inventive concept asdefined by the claims. The exemplary embodiments should be considered ina descriptive sense only and not for purposes of limitation. Therefore,the scope of the inventive concept is defined not by the detaileddescription but by the appended claims, and all differences within thescope will be construed as being included in the inventive concept.

What is claimed is:
 1. A video decoding method comprising: obtaining,from a bitstream, information about a maximum size of a coding unit;obtaining, from the bitstream, first information indicating whether adependent slice segment is permitted to be included in a picture;determining at least one maximum coding unit included in a first slicesegment, based on a maximum coding unit size, which is determined byusing the information about the maximum size; obtaining, from thebitstream, second information indicating whether a current maximumcoding unit is at an end of the first slice segment or not; determininga number of entry points of subsets, which are included in the firstslice segment, based on third information obtained from a slice segmentheader of the bitstream; determining positions of the entry points basedon fourth information obtained from the slice segment header, whichindicates a number that is less by 1 than an offset of the entry points;storing a context variable of the first slice segment if the firstinformation indicates that a dependent slice segment is permitted to beincluded in the picture and the second information indicates that thecurrent maximum coding unit is at the end of the first slice segment;obtaining fifth information, from the bitstream, which indicates whethera second slice segment is a dependent slice segment or not; and decodingthe second slice segment by using the stored context variable when thefifth information indicates that the second slice segment is a dependentslice segment, wherein the second slice segment is located next to thefirst slice segment, and wherein the number and the positions of theentry points are determined if a plurality of tiles are included in thepicture or synchronization can be performed for context variables of thecurrent maximum coding unit included in the picture.
 2. The videodecoding method of claim 1, wherein the storing of the context variablecomprises storing context variables of the current maximum coding unitif a dependent slice segment is permitted to be included in the picture.3. The video decoding method of claim 1, wherein the storing of thecontext variable comprises storing a context variable of the currentmaximum coding unit finally decoded in the first slice segment if thesecond information indicates that the current maximum coding unit is atthe end of the first slice segment.
 4. The video decoding method ofclaim 1, further comprising: determining whether a dependent slicesegment of the picture can be included or not based on the firstinformation obtained from a picture parameter set of the bitstream;determining whether the current maximum coding unit is a final maximumcoding unit or not based on the second information obtained from data ofthe current maximum coding unit among data of each of slice segments ofthe bitstream; and obtaining a bin string from the data of the currentmaximum coding unit.